You wrote: "if you have the exact measurements of the label, maybe it would add a bit more evidence one way or the other (but you're still a long way off proof)."
A good point, and to go with it, a cautionary note. Recently I received an image of three vases, one clearly bearing a "Bohemia" glass label. Proof-positive? Hardly, when all three vases were scandinavian, two clearly Riihimaki and the third probably from the same factory. I think the label had been re-used, to try to improve a price at auction.