Could Nothing But Alpha secretly change the record?

Not without it being detectable, once a day's fingerprint is published and copied by others. Before that, yes: we control our own machines and clock, so the hashes alone don't stop us. That's why the design relies on public anchoring and on copies we don't control, and why we say so.

Details

• We treat ourselves as the strongest adversary. We could, in principle, edit records and recompute every hash. A hash chain alone proves the ledger is internally consistent, not that its history wasn't rewritten.
• Publishing heads closes that. After day D's head is published, any edit, deletion, reordering, backdated insert or truncation on or before D changes the head, and verification against the published head fails.
• GitHub alone isn't enough, because the repository's owner controls its settings and commit dates are self-reported. Independent copies (GH Archive, Software Heritage, anyone's clone) are what make a rewrite detectable.
• Remaining gaps we're open about:
  • Records are only self-attested until that day's head is published, usually within about a day.
  • Anchor times are self-reported. A Bitcoin timestamp (OpenTimestamps) that would independently prove when a head existed is designed but not switched on.
  • Some rewrites are rejected outright by the verifier even if we recomputed everything: early resolution, faked scores, a duplicate resolution, or withdrawing a call after its window opened.