I'd doubt it -- things can speed up reactions but it's not generally THAT extreme. I know a dealer who has been in business for a LONG time and said it would take a ridiculous amount of time for it to happen. Since he has stuff sitting around for years in those flips sometimes and has been around for so long I trust his opinon. The guy I talked to today said the same thing. Still, the stuff in my SDB is either slabbed or in mylar, and nobody is moving that stuff around (and nothing in mylar is UNC anyway). I have coins like Morgans in UNC at home in flips in a binder but I'm not too concerned. I wouldn't use PVC for long-term storage though, and it sounds like stuff moving around a lot shouldn't be put into mylar. A lot of my collection is simply in Whitmans, but those aren't my 65+ investment-grade coins. Generally if something is over $500 it's slabbed anyway (and if it's not, chances are there's a problem with it). ~ Ricky