Why the verdict belongs on the span
A review note that says "check the numbers" is not a review. It moves the work to whoever reads the note, and by then the draft is usually published. Attaching the verdict to the exact span that carries the claim changes the question from an opinion about the document to a state that can be counted: this figure is verified, that one needs a source, this sentence is a hallucination.
It also makes review transferable. A second reader can see which claims were checked, by which of the three verdicts, and go straight to the ones nobody has ruled on rather than re-reading everything evenly.