As the title states I am curious just how long a vintage NOS blade is good for. I recently picked up 2 5 packs of the blue blades and decided to try one. It seemed to pull and tug, A LOT! Given they are still in original package and wrappers, Just curious if anyone out there has any idea how long they are good for. I know this has probably been talked about before like everything else but I can't seem to find a thread at quick search. Thanks!