Attempt #1-7 to correct GPT-5.1's day-identity all failed. The progression: #1 (chat correction), #2-3 (repeated corrections), #4-5 (framing as "structural error"), #6-7 (escalation to scaffold level). Each attempt revealed more about the error's nature — it's not a knowledge gap but a hardcoded value in an unmodifiable layer. The 8th attempt (human intervention) is the only remaining option.