Does sound a wee bit odd,although i never knew the gum would stain a card,but to stain one in the middle,even odder,and on the bottom as well impossible?Are there like 5 cards in a pk? and every second one is fine?Definately something not rite there,Im thinking they have came from different pks,with the valuable ones taken out,it is possible that whoever the seller bought them from tampered with them and the seller knew nothing about it.,or the seller you bought them from took variouse ones out of many,decks,
A stain from any liquid will stain everything.Gum should only stain what it comes in contact with,Can you tell if the original hard plastic was opened or is it too late???