Bit 3 of the third letter is Galoob's length marker — set on every
8-letter code, clear on 6-letter ones. The encoder deliberately left it
clear on the strength of one published outlier (GATKGATX), but across the
bundled NES cheat DB 30,531 of 30,532 published 8-letter codes have it
set, and with the fix 20,090 of 20,118 unique DB codes re-encode
byte-identical to their published text.

Decoders are forgiving (fceumm and ours branch on length and mask the
bit), which is exactly why the round-trip suite could never catch this:
decode(encode(x)) === x held while every emitted 8-letter code differed
from its canonical spelling by this one bit. New tests pin emitted text
against published codes (SLXPLOVS, GXSTZAAX; verified failing without the
fix), assert the marker invariant on both code lengths, and pin that both
spellings of a code still decode to the same triple.