'58 Topps BB question for those who have handled many raw cards...

RTB

I bought the '58s as a kid and completed the set. Whenever I go through them I notice a strange sort of defect in the cardboard on the lower left side of some cards, like maybe 30 or 40 in all. It is a very slight raised area or welt that you can feel and see at an angle under the light. The size of the area can be an inch or two high by the same in width. It looks like it may be from a water stain or something. I suppose it could be something I did but there is no logical reason why I would have grouped these particular cards form various series together. Furthermore, I had one of them graded a couple years ago (a yellow letter Clemente) and it got a straight PSA 5 which is what it deserved based on corners etc.

Has anyone else noticed this? If not, then it must be something I did, but believe me, that would be something I think I'd remember!