A coin with PVC (or polyvinylchloride) damage, if caught early enough can be corrected without harm to the coin. The PVC leaves a greenish tone/surface which can usually be removed by dipping the coin in acetone, having the coin professionally restored, (recommended) or other professional coin cleaning products.
Coins stored in older 2x2 vinyl flips, experience a chemical reaction which causes the green toned PVC problem. If you submit a coin and it is returned because of PVC damage, do not worry, the coin can usually be fixed either through NCS or dipping it yourself. It takes years for PVC to damage coins to the point they are ruined. Remember to always use mylar 2x2 flips instead of PVC flips. The material is not quite as strong, but your coins will thank you!
Some vamworld.com users have been VERY successful at resubmitting a PVC damaged coin after having the coin professionally conserved (cleaned), and getting it successfully graded after a second, third, and sometimes even a fourth or fifth attempt at sending it in. So do not necessarily give up on a coin which comes back with a note of PVC damage. Persistence is the key if you truly believe your coin is "original". Below are some visual examples of SEVERELY PVC damaged coins.
Here are some visual examples of PVC damage on a coin. (images provided by nevst)
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