Implement Nebraska State Supplementary Payment (SSP)

[hua7450]

Summary

Implements Nebraska's State Supplementary Payment — Aid to the Aged, Blind, or Disabled — Payment (AABD-PMT) — a state-administered, state-funded "fill-the-gap" supplement that brings SSI recipients up to a living-arrangement-specific standard of need.

Closes #8234

Regulatory Authority

• Neb. Rev. Stat. § 68-1001 (AABD program statutory basis, 1965; SSI/SSP integration since 1974) and § 68-1005 (companion SDP) — https://nebraskalegislature.gov/laws/statutes.php?statute=68-1005
• Title 469 Nebraska Administrative Code (469 NAC) — https://dhhs.ne.gov/Documents/Title-469-Complete.pdf
• 469-000-211 (Standard of Need / payment standards) — https://dhhs.ne.gov/Documents/469-000-211.pdf (effective 2021-01-01, still in effect; historical 2015 / 2017 versions via Wayback Machine)
• 469-000-207 (SSI Federal Benefit Rate reference) — https://dhhs.ne.gov/Documents/469-000-207.pdf
• SSA "State Assistance Programs for SSI Recipients, January 2011" — Nebraska — https://www.ssa.gov/policy/docs/progdesc/ssi_st_asst/2011/ne.pdf#page=1 (program description) and https://www.ssa.gov/policy/docs/progdesc/ssi_st_asst/2011/ne.pdf#page=2 (Table 1 rates and living-arrangement definitions)

Program Overview

• Administration: State-administered (Nebraska DHHS pays the supplement directly; SSA does not bundle it with the federal SSI check)
• Funding: State funds
• Payment model: Standard-of-need-based fill-the-gap, not a flat SSP. Payment = (standard of need + actual shelter expense capped at max, or alternate-living standard) − federal SSI FBR − other countable income, floored at zero. Per 469 NAC 3-006.02B1a / 3-006.02B3a(1)(a), the independent budget uses actual shelter expense up to the single/multiple shelter cap; shelter includes rent and home ownership expenses (469 NAC 3-004.02).
• Current caseload: 5,437 recipients in 2009; 2010 state-administered SSP expenditures of $6,260,403 (SSA 2011 NE report — https://www.ssa.gov/policy/docs/progdesc/ssi_st_asst/2011/ne.pdf#page=2)

Eligibility

Requirement	Source	How Modeled
Must actually receive SSI	469 NAC 3-006.01A; AABD-PMT supplement specifically for SSI recipients	ssi > 0 (already implies is_ssi_eligible + federal income test + takeup)
Must reside in Nebraska	469 NAC 2-003	defined_for = StateCode.NE
Aged 65+ OR blind/disabled (SSI definition)	469 NAC 2-005, 2-007	Implied by ssi > 0
Citizenship / qualified alien	469 NAC 2-002	Implied by ssi > 0
Federal SSI resource rules	469 NAC 2-009	Implied by ssi > 0
Federal SSI income rules + state fill-the-gap	469 NAC 2-010, 3-006.01A	Fill-the-gap: max_(0, total_budget − uncapped_ssi)

Benefit Amounts (469 NAC 469-000-211 — https://dhhs.ne.gov/Documents/469-000-211.pdf)

Independent Standard of Need (added to actual shelter expense, capped at max shelter allowance)

Effective	1 person	2 persons	3	4	Each addl
2015-01-01	$491	$778	$964	$1,155	$191
2017-01-01	$505	$799	$989	$1,186	$198
2021-01-01 (frozen through 2025)	$564	$887	$1,109	$1,336	$222

Max Shelter Allowance (Independent only, frozen since 2015)

Single	Multiple
$281	$349

Alternate-Living Standards (monthly; PNA $64 embedded)

Living arrangement	2015	2017	2021–2025
Long-term care (NH, ICF/MR, hosp acute, IMD) — Medicaid pays PNA	$50	$60	$60
Board & Room / Boarding Home / Drug Treatment Center	$737	$739	$798
Certified Adult Family Home	$865	$867	$926
Licensed Assisted Living Facility / Mental Health Center	$1,175	$1,177	$1,236
Assisted Living Waiver (AD/TBI)	$733	$735	$794
Licensed Group Home (children/disabled)	$801	$803	$862
Licensed Center for Developmentally Disabled	$737	$739	$798

The 9 living arrangements in 469-000-211 collapse to 7 distinct alternate-living rate values plus an INDEPENDENT and NONE enum entry. Rates that always co-move (Board & Room, Boarding Home, Drug Treatment Center; Assisted Living Facility and Mental Health Center; Center for Developmentally Disabled and Boarding Home) share enum values.

Couple treatment: Joint 2-person Independent standard of need split 50/50 between spouses living together. Couples in any alternate-living arrangement are treated as two individuals (per SSA 2011 PDF Table 1 footnote a: "Couples are treated as two individuals starting with the month after leaving an independent living arrangement" — https://www.ssa.gov/policy/docs/progdesc/ssi_st_asst/2011/ne.pdf#page=2).

Personal Needs Allowance: $64 PNA is embedded in all alternate-living standards (matches NAC structure). Long-Term Care = $60 because Medicaid covers the PNA in those settings.

No federal Code B / ISM tier: Per SSA 2011 PDF page 1, "Persons living in the household of another receive the same state supplement as those living independently." Nebraska pays the Independent standard regardless of household-of-another status.

COLA: No automatic indexing. Standards frozen at 2021 values since 2021-01-01 through at least 2025.

Couple gating

A combined 2-person Independent budget is used only when all three conditions are met:

• ssi_claim_is_joint (joint SSI claim)
• both spouses are SSI-eligible
• both spouses share the same Independent living arrangement

Otherwise, each spouse's AABD payment is computed individually (per SSA 2011 footnote a).

Not Modeled (by design)

What	Source	Why Excluded
State Disability Program (SDP) companion program	Neb. Rev. Stat. § 68-1005; 469 NAC	Separate program for non-SSI-eligible disabled individuals failing the 12-month durational test — separate PR
Special requirements (service animal $50/mo, etc.)	469 NAC 3-004.03	One-off allowances; small effect; deferred
Blind earned-income $20 add-back	469 NAC 3-006.01A1	Small effect; requires blind-earned-income tracking
Additional NE-only countable income subtraction	469 NAC 3-006.01A	Requires NE-specific income tracking beyond federal SSI countable income
Institutionalization rules (prison / public institution)	469 NAC 2-008	We don't track prison/public-institution residency at the moment
3rd-party medical cooperation	469 NAC 2-011	Administrative — not simulatable
No-other-categorical-assistance check	469 NAC 2-013	Administrative — not simulatable
Relative responsibility (beyond spouse-for-spouse)	469 NAC 2-006	Spouse-for-spouse already handled by SSI deeming; broader relative responsibility administrative
SSI + VA spouse separation	469 NAC 3-005.02 / 2-006.01	Rare; depends on VA Aid & Attendance modeling
Alternate-care spouse separations	469 NAC 3-006.02	Complex separations beyond couple split; deferred
State Assistance for Special Needs (transportation, furniture, etc.)	SSA 2011 NE PDF page 1	Separate need-based program, not SSP

Files

policyengine_us/parameters/gov/states/ne/dhhs/aabd/
  alternate_living_standard.yaml
  shelter_allowance/single.yaml
  shelter_allowance/multiple.yaml
  standard_of_need/independent.yaml

policyengine_us/variables/gov/states/ne/dhhs/aabd/
  ne_aabd.py
  ne_aabd_alternate_living_arrangement.py
  ne_aabd_couple_rate_applies.py
  ne_aabd_eligible.py
  ne_aabd_living_arrangement.py
  ne_aabd_standard_of_need.py

policyengine_us/tests/policy/baseline/gov/states/ne/dhhs/aabd/
  integration.yaml
  ne_aabd_eligible.yaml
  ne_aabd_living_arrangement.yaml

Plumbing updated: policyengine_us/variables/household/income/spm_unit/spm_unit_benefits.py, policyengine_us/parameters/gov/household/state_benefits/household_state_benefits.yaml, and policyengine_us/programs.yaml.

Note on naming: Variable prefix is ne_aabd_* (matching Nebraska's official program name "Aid to the Aged, Blind, or Disabled"), not the generic ne_ssp_* convention used in some other states.

Historical Notes

• 2015 → 2017: ~3% increase across most standards
• 2017 → 2021: ~12% increase across most standards
• 2021 → 2025: frozen at 2021 values
• Long-Term Care PNA: $50 in 2015, raised to $60 in 2017 and held since
• Independent / alternate-living PNA: $64 from 2015 onward (raised from $60 referenced in SSA 2011 PDF)

Verification TODO

• Verify payment amounts against 469 NAC 469-000-211 — https://dhhs.ne.gov/Documents/469-000-211.pdf
• Verify eligibility logic against 469 NAC chapters 2 and 3-006.01 — https://dhhs.ne.gov/Documents/Title-469-Complete.pdf
• Verify amounts current as of 2015–2025 (three effective-date tiers)
• Verify alternate-living-couple two-individuals rule against SSA 2011 PDF Table 1 footnote a — https://www.ssa.gov/policy/docs/progdesc/ssi_st_asst/2011/ne.pdf#page=2
• CI passes

Test plan

• 38 tests pass across ne_aabd_eligible.yaml, ne_aabd_living_arrangement.yaml, and integration.yaml (includes new $0 / below-cap / at-cap / above-cap shelter scenarios for the actual-shelter-capped-at-max behavior)
• Microsim regression: clean
• CI passes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.69%. Comparing base (8cb60e7) to head (a8e7e79).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #8235      +/-   ##
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===========================================
  Files            3        7       +4     
  Lines           63      113      +50     
  Branches         0        2       +2     
===========================================
+ Hits            63      107      +44     
- Misses           0        6       +6     

Flag	Coverage Δ
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[PavelMakarchuk]

Program Review — PR #8235 (Nebraska AABD-PMT / State Supplementary Payment)

Source Documents

• PDF 1: 469 NAC 469-000-211 — Standard of Need (current, eff. 2021-01-01) (1 page)
• PDF 2: SSA 2011 SSI State Assistance — Nebraska (3 pages, via Wayback)
• PDF 3: 469 NAC 469-000-207 — SSI FBR (1 page)
• PDF 4: Title 469 NAC Complete (147 pages)
• PDF 5: 469-000-211 eff. 2017-01-01 (Wayback)
• PDF 6: 469-000-211 eff. 2015-01-01 (Wayback)
• Statute: Neb. Rev. Stat. § 68-1001 / § 68-1005
• Year: 2015-2025 (three effective-date tiers)
• Scope: PR changes only

---

Critical (Must Fix)

C1. ne_aabd income_excess uses federal SSI countable-income definition with disregards that NAC 3-006.01A explicitly forbids

• Files:
  • /Users/pavelmakarchuk/policyengine-us/policyengine_us/variables/gov/states/ne/dhhs/aabd/ne_aabd.py (lines 25–29)
  • Path: ne_aabd → uncapped_ssi → ssi_countable_income (applies $20 general, $65 earned, 50% earned disregards plus ISM/PMV and deeming).
• Regulatory citation: 469 NAC 3-006.01A (Title-469-Complete.pdf, lines 5458–5481) enumerates the closed list of available net income: (a) non-spouse Essential Person income, (b) VA Aid & Attendance, (c) income allocated from another assistance unit, (d) ineligible-spouse income not used by SSI — and explicitly states "This income is not allowed the $20 general income disregard."
• Code-path verification: CONFIRMED (/tmp/review-program-codepath-2.md). For SSI-only households income_excess == 0 and the bug is invisible. It bites materially for:
  1. SSI recipients with earned income (federal disregards understate countable income vs NAC → over-pays supplement)
  2. Recipients with VA Aid & Attendance (NAC denies the $20 disregard; code applies it)
  3. Households with non-spouse Essential Persons (NAC counts their income; code ignores it entirely)
  4. Joint-claim couples with deemed ineligible-spouse income
  5. ISM/PMV-affected recipients
• Suggested fix: introduce ne_aabd_countable_income summing only (a)–(d) with no $20 disregard, subtract from requirements first, then subtract the FBR (matches the NAC's two-step order — see C2 below for the order-of-operations sub-issue).
• Anchor: Title-469-Complete.pdf#page=126.

C2. ne_aabd_alternate_living_arrangement declared YEAR while every downstream consumer is MONTH

• File: /Users/pavelmakarchuk/policyengine-us/policyengine_us/variables/gov/states/ne/dhhs/aabd/ne_aabd_alternate_living_arrangement.py (line 11) — definition_period = YEAR.
• Consumers (ne_aabd_living_arrangement.py:42 reads via person.this_year; the outer variable is MONTH); downstream ne_aabd_standard_of_need, ne_aabd_couple_rate_applies, ne_aabd are all MONTH.
• Regulatory citation: 469 NAC 3-006.02B5 contemplates monthly entry/exit from care facilities; the NE budget is computed monthly.
• Effect: a user cannot model someone who is ASSISTED_LIVING_FACILITY for half the year and INDEPENDENT for the other half — the year-scoped input resolves to one value for the entire year, preventing mid-year transitions.
• Suggested fix: switch definition_period to MONTH to match the monthly budgeting cadence and align all dependents.

---

Should Address

S1. ne_aabd_eligible uses ssi > 0, excluding 1619(b) recipients and grandfathered non-SSI AABD pathway

• File: /Users/pavelmakarchuk/policyengine-us/policyengine_us/variables/gov/states/ne/dhhs/aabd/ne_aabd_eligible.py (line 21).
• ssi (YEAR) multiplies by takes_up_ssi_if_eligible, which is assigned at microdata-build time. A fully SSI-eligible person flagged non-takeup yields ssi == 0 and therefore ne_aabd_eligible == false.
• Also excludes 1619(b) SSI recipients (zero cash but Medicaid-eligible — NAC lines 656, 672–673, 5440–5441) and grandfathered non-SSI recipients listed in 469 NAC 3-006.01 / SSA PDF Table 2 note ("Includes certain grandfathered, non-SSI recipients who meet state eligibility criteria").
• Reference pattern: AL / ME / MA SSP variables gate on uncapped_ssi > 0 (or is_ssi_eligible).
• Citation: 469 NAC 2-010 + 3-006.01A.

S2. Order of operations in fill-the-gap conflates two NAC steps

• File: /Users/pavelmakarchuk/policyengine-us/policyengine_us/variables/gov/states/ne/dhhs/aabd/ne_aabd.py (returns max_(0, standard_of_need - federal_ssi - income_excess)).
• Citation: 469 NAC 3-006.01A specifies (1) requirements − available net income → "budgetary need", then (2) subtract FBR (3-006.01A1). Repo collapses both into a single floor; for borderline cases the determination diverges from the NAC's "deny at step 1 if income ≥ requirements".
• Closely related to C1's fix path.

S3. Parameter description includes forbidden phrase "by household size" and redundant "monthly"

• Files:
  • /Users/pavelmakarchuk/policyengine-us/policyengine_us/parameters/gov/states/ne/dhhs/aabd/standard_of_need/independent.yaml (line 1) — drop "by household size" (evident from breakdown)
  • All four parameter files (alternate_living_standard.yaml, shelter_allowance/single.yaml, shelter_allowance/multiple.yaml, standard_of_need/independent.yaml) — drop redundant "monthly" (evident from period: month).
• Skill rules: policyengine-parameter-patterns explicitly forbids both.

S4. Family-size 3+ values in standard_of_need/independent.yaml are dead code

• File: /Users/pavelmakarchuk/policyengine-us/policyengine_us/parameters/gov/states/ne/dhhs/aabd/standard_of_need/independent.yaml (sizes 3–10).
• ne_aabd_standard_of_need.py hard-codes independent_size = where(couple_applies, 2, 1); sizes ≥3 are never indexed.
• Either:
  • implement Essential Person inclusion (469 NAC 3-006.02 / 3-006.02B2) so the larger SoN brackets apply, or
  • prune sizes 3–10 from the parameter file with a comment that EP inclusion is deferred.

S5. Missing statute citation (Neb. Rev. Stat. § 68-1001 / § 68-1005)

• No parameter file or variable reference tuple cites the statutory authority. Add a 4th tuple entry to ne_aabd_eligible.py and ne_aabd.py:

  "https://nebraskalegislature.gov/laws/statutes.php?statute=68-1005"
  

S6. Title-469 #page=130 anchor on ne_aabd_couple_rate_applies.py should be #page=129

• File: /Users/pavelmakarchuk/policyengine-us/policyengine_us/variables/gov/states/ne/dhhs/aabd/ne_aabd_couple_rate_applies.py.
• Page 129 carries the heading 3-006.02B3a(1) Spouse on AABD or SDP and the "payment is divided equally" rule the code comment cites. Page 130 is the (1)(a) Living Independently subsection. Either change anchor to #page=129 or change cited section to 3-006.02B3a(1)(a).

S7. Missing 2017 reference on shelter allowance parameter files

• shelter_allowance/single.yaml and multiple.yaml only reference the 2021 and 2015 versions. Values ($281 / $349) are unchanged through 2017, but the 2017 manual letter should be cited as continuing evidence (Wayback URL).

S8. Three alternate-living rates (BOARD_AND_ROOM, ASSISTED_LIVING_WAIVER, GROUP_HOME_CHILDREN) lack numeric verification in tests

• ne_aabd_living_arrangement.yaml Cases 5–7 only assert the enum propagates; they never verify ne_aabd_standard_of_need or ne_aabd dollar amounts at those arrangements. 3 of 7 alternate-living rates have zero numeric coverage.

S9. 2015-tier values never directly tested

• Earliest test period is 2016-01 (Case 8a), which resolves to the 2015 tier — but no test sets period: 2015-01 literally. None of the distinct 2015-tier alternate-living rates ($50 LTC, $865 AFH, $737 BR, $1,175 ALF, $733 ALW, $801 GHC) are exercised.

S10. ssi_claim_is_joint = False with both-SSI-eligible + both-INDEPENDENT branch untested

• ne_aabd_couple_rate_applies truth table has 8 input combinations; this single AND-gate branch (joint_claim=F, both_eligible=T, both_independent=T) is not exercised.

S11. Unlicensed board-and-room couple sub-case not separately handled

• Citation: 469 NAC 3-006.02B3a(1)(b). Code treats every alternate-living person as a standalone individual; this matches SSA 2011 footnote a for licensed alternate living but is too coarse for the unlicensed board-and-room couple sub-case (single combined budget).

S12. Missing dedicated unit-test YAML for ne_aabd_standard_of_need.py, ne_aabd_couple_rate_applies.py, and ne_aabd.py

• All three have conditional/branching logic but are only exercised via integration tests. Per policyengine-testing-patterns, dedicated unit-test files would make the regression surface explicit (income_excess in particular).

S13. Redundant title formatting 469 NAC 469-000-211 in all four parameter files

• 469-000-211 is the document number within Title 469 NAC; the leading 469 NAC duplicates the prefix. Use Title 469 NAC § 469-000-211 or similar.

---

Suggestions

G1. ne_aabd_standard_of_need.py line 39 — independent_total / 2 → independent_total / marital_unit.nb_persons()

• Magic number 2 is acceptable per code-style skill ("basic math") but nb_persons() would be more vectorization-correct and self-documenting.

G2. ne_aabd_living_arrangement could be YEAR

• Formula only accesses YEAR inputs (ssi_federal_living_arrangement, ne_aabd_alternate_living_arrangement); declaring it YEAR would be cheaper and aligned. (Decision interacts with C2.)

G3. ne_aabd.py local variable federal_ssi = ssi_amount_if_eligible — rename for clarity

• Returns the post-VTR / post-Code-D amount. Renaming to effective_federal_payment and adding a comment that NAC intends the adjusted FBR (which is what the code uses, and is regulation-consistent in both directions) would prevent confusion.

G4. ne_aabd_alternate_living_arrangement.py lacks docstring explaining why it exists separately from ne_aabd_living_arrangement

• The split (input enum vs derived enum that overlays federal Code D) is correct but unobvious; add a short comment.

G5. Living arrangement enum collapses 9 NAC categories to 7

• Reasonable for now; consider a comment near the enum (not only in the PR description) noting the collapse for future maintainers.

G6. verified_years: "2015-2025" in programs.yaml may overstate verification

• 2018–2020 has no published manual letter; the PR assumes the 2017 rates carried through. Consider "2015-2017, 2021-2025" or document the assumption.

G7. INDEPENDENT: 0 / NONE: 0 entries in alternate_living_standard.yaml are sentinels

• Only read on the false branch of where. Either drop them or refactor to select(...) to avoid the unused parameter rows.

G8. Manual Letter number for 2021 tier not stated in reference

• Historical references cite "Manual Letter #1-2017" / "#74-2014"; the 2021 reference does not. Adding the Manual Letter number (likely #41-2020 or #1-2021) would symmetrize the citation block.

G9. Deferred features (intentional)

• SSI service-animal $50 maintenance allowance (469 NAC 3-004.03)
• Essential Person inclusion (469 NAC 3-006.02 / 3-006.02B2) — would unlock SoN sizes 3–10
• Pro-ration for spouse on ADC/RRP (469 NAC 3-006.02B3a(2)(a))
• Pro-ration for shared housing with self-supporting roommates (469 NAC 3-006.02B4a)
• Three-month continuous LTC budgeting override (469 NAC 3-006.01A2) — time-history rule, single-period architecture limitation
• SSI referral amounts and standalone PNA $64 parameter

G10. Inline-comment-heavy style

• Per code-style skill, multi-line regulatory explanations belong in reference URLs and PR description rather than inline. Borderline — current comments document non-obvious modeling choices (e.g., the income_excess rationale, the is_ssi_eligible choice to avoid circularity); kept-or-trimmed at author discretion.

G11. Integration test numbering gaps (Case 9 → 11, Case 17 → 19)

• Either renumber for continuity or add the missing cases.

---

Investigated and Cleared

Circular dependency ne_aabd ↔ ssi via housing_cost → rent → housing_assistance → hud_annual_income — REJECTED

• Initial regulatory review (C1 in /tmp/review-program-regulatory.md) flagged a cycle: ne_aabd_standard_of_need → housing_cost → rent → housing_assistance → hud_hap → hud_annual_income → ssi → ... → ne_aabd.
• Code-path verification (/tmp/review-program-codepath-1.md) traced every edge and confirmed: nothing in the SSI subtree reads housing_cost, housing_assistance, hud_annual_income, spm_unit_benefits, or ne_aabd. SSI is a source relative to this subgraph; the chain is a deep one-way DAG that terminates inside SSI's earned/unearned income inputs.
• The only external reference to ne_aabd is spm_unit_benefits.py:32, which is a terminal sink (not consumed by SSI or HUD).
• Verdict: No cycle. The reviewer correctly identified a long dependency chain but missed that it never closes.

---

PDF Audit Summary

Category	Count
Confirmed correct values	50 (all SoN, alternate-living, shelter caps across 2015/2017/2021 tiers)
Mismatches (code-path confirmed)	1 (income_excess)
Mismatches rejected (code-path cleared)	1 (circular dependency — C1)
Unmodeled items (intentional deferrals OK)	4-5 (1619(b), grandfathered AABD, service animal, EP additional persons, etc.)

---

Validation Summary

Check	Result
Regulatory Accuracy	1 critical + 5 should
Reference Quality	0 critical + 5 should
Code Patterns	0 critical + 2 should
Test Coverage	0 critical + 5 should
PDF Value Audit	0 mismatches / 50 confirmed
CI Status	24/25 passing — only codecov/project harmless

---

Review Severity: REQUEST_CHANGES

Reason: income_excess uses the wrong income-disregard semantics for households with earned income, VA A&A, ISM, parental deeming, or a non-spouse EP — over-pays in those cases. Period mismatch on ne_aabd_alternate_living_arrangement (YEAR while inputs are MONTH) prevents mid-year transitions. Both have concrete fixes.

---

Next Steps

To auto-fix issues: /fix-pr 8235

[hua7450]

Thanks for the thorough review, Pavel. Want to push back on C1's severity.

You're right that 469 NAC 3-006.01A enumerates a closed list of "available net income" and explicitly forbids the $20 disregard — verified against Title-469-Complete.pdf#page=126. But I want to push back on the "5 categories of over-payment" framing:

income_excess = max_(0, -uncapped_ssi) = max_(0, ssi_countable_income - ssi_amount_if_eligible)

For any person where ne_aabd_eligible == True we already gate on ssi > 0. ssi > 0 ⇒ ssi_amount_if_eligible > ssi_countable_income by SSI's own definition ⇒ income_excess == 0 always.

So the five scenarios listed don't fire in practice:

• Earned income, ISM/PMV, parental/spousal deeming — all yield countable ≤ amount_if_eligible for SSI recipients, so income_excess = 0. Code and NAC produce identical supplements (SoN − FBR).
• VA Aid & Attendance — not currently tracked in policyengine-us (grep returns no variable).
• Non-spouse Essential Person income — EP inclusion isn't modeled (your own S4); the SoN size is fixed at 1 or 2 anyway.
• Allocated income from another assistance unit — not tracked.

So income_excess was a no-op being passed through a non-trivial formula. Rather than implement a closed list whose four inputs don't exist in the model, I deleted the line and added a comment documenting NAC 3-006.01A's closed list as an unmodeled-feature. If/when we add VA A&A or EP support, the offset goes back in cleanly.

I'd suggest downgrading C1 from "Critical" to "Should — document modeling limitation". Happy to be overruled if I'm missing a case.