diff --git a/__test__/at.test.ts b/__test__/at.test.ts
index b68d6ef..a9daea4 100644
--- a/__test__/at.test.ts
+++ b/__test__/at.test.ts
@@ -179,15 +179,28 @@ describe("at.vnr", () => {
     }
   });
 
-  test("invalid birth date (month > 12)", () => {
+  // VNRs may legitimately encode "month > 12" when the
+  // daily-serial pool for a substitute date is exhausted
+  // (per sozialversicherung.at). Month is therefore not
+  // calendar-checked; only the checksum is gating.
+  test("month-13 with matching checksum is valid", () => {
+    const r = at.vnr.validate("1234011380");
+    expect(r.valid).toBe(true);
+    if (r.valid) expect(r.compact).toBe("1234011380");
+  });
+
+  test("month-13 with non-matching checksum fails on checksum", () => {
     const r = at.vnr.validate("1237011380");
     expect(r.valid).toBe(false);
     if (!r.valid) {
-      expect(r.error.code).toBe("INVALID_COMPONENT");
+      expect(r.error.code).toBe("INVALID_CHECKSUM");
     }
   });
 
-  test("invalid birth date (day 0)", () => {
+  // Day, by contrast, is always 01-31 per the source —
+  // even substitute and overflow VNRs use day "01" —
+  // so day "00" is rejected as a component error.
+  test("day-0 is invalid", () => {
     const r = at.vnr.validate("1237000180");
     expect(r.valid).toBe(false);
     if (!r.valid) {
@@ -195,6 +208,14 @@ describe("at.vnr", () => {
     }
   });
 
+  test("leading-zero serial is invalid", () => {
+    const r = at.vnr.validate("0000000000");
+    expect(r.valid).toBe(false);
+    if (!r.valid) {
+      expect(r.error.code).toBe("INVALID_COMPONENT");
+    }
+  });
+
   test("format adds space", () => {
     expect(at.vnr.format("1237010180")).toBe("1237 010180");
   });
diff --git a/__test__/us.test.ts b/__test__/us.test.ts
index 01eda5a..de07c6d 100644
--- a/__test__/us.test.ts
+++ b/__test__/us.test.ts
@@ -265,12 +265,13 @@ describe("us.rtn", () => {
     }
   });
 
-  test("invalid prefix (00)", () => {
-    const r = us.rtn.validate("001000021");
-    expect(r.valid).toBe(false);
-    if (!r.valid) {
-      expect(r.error.code).toBe("INVALID_COMPONENT");
-    }
+  // Prefix 00 is reserved for U.S. Government and
+  // federal agencies per the ABA Routing Number Policy
+  // (https://en.wikipedia.org/wiki/ABA_routing_transit_number).
+  test("valid prefix (00, U.S. Government)", () => {
+    const r = us.rtn.validate("000000026");
+    expect(r.valid).toBe(true);
+    if (r.valid) expect(r.compact).toBe("000000026");
   });
 
   test("invalid prefix (13)", () => {
diff --git a/src/at/vnr.ts b/src/at/vnr.ts
index 0dce509..8360c66 100644
--- a/src/at/vnr.ts
+++ b/src/at/vnr.ts
@@ -6,8 +6,19 @@
  * The check digit is computed using a weighted sum
  * mod 11 over the 9 non-check digits.
  *
+ * The 6-digit "birth date" field is not always a real
+ * calendar date. Sozialversicherung.at documents that
+ * persons with unknown date of birth are issued
+ * substitute values (01.01. or 01.07.), and that
+ * months 13, 14, etc. are issued when the daily serial
+ * pool for a given substitute date is exhausted. We
+ * therefore do not enforce a calendar-valid month here.
+ * The day field, however, is always within 01-31 — even
+ * in the documented overflow cases the day stays "01"
+ * — so we keep the day-bounds check.
+ *
  * @see https://de.wikipedia.org/wiki/Sozialversicherungsnummer#%C3%96sterreich
- * @see https://www.sozialversicherung.at/
+ * @see https://www.sozialversicherung.at/cdscontent/?contentid=10007.820902&viewmode=content
  */
 
 import type { ValidateResult, Validator } from "../types";
@@ -44,13 +55,24 @@ const validate = (value: string): ValidateResult => {
     );
   }
 
-  // Validate birth date (DDMMYY in positions 4-9)
+  // Per sozialversicherung.at, the 3-digit serial
+  // (positions 0-2) never starts with zero.
+  if (v[0] === "0") {
+    return err(
+      "INVALID_COMPONENT",
+      "Austrian VNR serial must not start with zero",
+    );
+  }
+
+  // Day (positions 4-5) is always within 01-31, even
+  // in the documented substitute and overflow cases
+  // where the month is shifted. The month is left
+  // unchecked per the source.
   const day = Number(v.slice(4, 6));
-  const month = Number(v.slice(6, 8));
-  if (day < 1 || day > 31 || month < 1 || month > 12) {
+  if (day < 1 || day > 31) {
     return err(
       "INVALID_COMPONENT",
-      "Austrian VNR contains an invalid birth date",
+      "Austrian VNR day field must be within 01-31",
     );
   }
 
@@ -88,7 +110,9 @@ const format = (value: string): string => {
 /** Generate a random valid Austrian VNR. */
 const generate = (): string => {
   for (;;) {
-    const serial = randomDigits(3);
+    // Serial must not start with zero (see validate).
+    const serial =
+      String(randomInt(1, 9)) + randomDigits(2);
     const day = String(randomInt(1, 28)).padStart(2, "0");
     const month = String(randomInt(1, 12)).padStart(2, "0");
     const year = String(randomInt(0, 99)).padStart(2, "0");
diff --git a/src/us/rtn.ts b/src/us/rtn.ts
index 8b4cda2..9232d49 100644
--- a/src/us/rtn.ts
+++ b/src/us/rtn.ts
@@ -7,9 +7,9 @@
  * [3, 7, 1] repeated three times.
  *
  * The first two digits identify the Federal Reserve
- * district (01-12) or special ranges (21-32 for
- * thrifts, 61-72 for electronic, 80 for traveler's
- * cheques).
+ * district (01-12) or special ranges (00 for U.S.
+ * Government, 21-32 for thrifts, 61-72 for electronic,
+ * 80 for traveler's cheques).
  *
  * @see https://en.wikipedia.org/wiki/ABA_routing_transit_number
  * @see https://www.frbservices.org/
@@ -48,7 +48,11 @@ const validate = (value: string): ValidateResult => {
   // Validate Federal Reserve prefix (first 2 digits)
   const prefix = Number(v.slice(0, 2));
   const validPrefixRanges =
-    (prefix >= 1 && prefix <= 12) ||
+    // 00 is reserved for U.S. Government and federal
+    // agencies per the ABA Routing Number Policy;
+    // 01-12 are the 12 Federal Reserve districts.
+    // @see https://en.wikipedia.org/wiki/ABA_routing_transit_number
+    (prefix >= 0 && prefix <= 12) ||
     (prefix >= 21 && prefix <= 32) ||
     (prefix >= 61 && prefix <= 72) ||
     prefix === 80;
@@ -78,7 +82,7 @@ const format = (value: string): string => compact(value);
 
 /** All valid Federal Reserve prefix ranges. */
 const PREFIX_RANGES: readonly [number, number][] = [
-  [1, 12],
+  [0, 12],
   [21, 32],
   [61, 72],
   [80, 80],