I have had some experience with vinyl (PVC) album pages. When stored for prolonged periods, the plasticizer in the PVC leaches out of the album page and into the mylar film of the 2x2. After a relatively short while, the outer surface of the 2x2 becomes sticky. This will not only make the coin difficult to remove from the album page, but will also pick up dirt and dust from whatever surface the sticky 2x2 is placed on - which in turn makes the coin inside look much uglier than it really is.
I have not known the plasticizer to pass all the way through the mylar film and attack the coin itself, but I don't doubt that given enough time (over a decade), it could do so.