Granted, I am not an object conservator, but in the world of paper and photographic conservation PVA is not considered a reversible adhesive. It is never used on a collection item, although some grades may be used to construct housings. Some of the commercial catalogs have identified PVA adhesive as “reversible” and that it “cleans up with water” but this is only true within a vary limited time period – within minutes. Keep in mind that the purpose of those catalogs are to sell products, so a bit a skepticism is appropriate. I agree wholeheartedly with Bruce. You are dealing with inherent vice, store it flat in a controlled environment, and consult a conservator.