The different size from the regular sticker set - it measures 3.25" x 5.25"-and the lack of the die cut would normally make us think it was a proof, but it does have a sticker back - so possibly a test? We don't know, and in this case, the Vault COA doesn't give us any additional clues. The front of the sticker is raised slightly where the two pieces of the adhesive cover on the back come together.
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