An example for consideration......
Many years ago, at the Ft Washington Show, I submitted this T206 Walter Johnson to SGC. I was quite disappointed
with the grade they gave it.
So I inquired. Derek Grady, who was the grader of it at that time, pointed out to me (under magnification) that there
was a very faint smear of a tiny glue spot (almost invisible) on this card's back.
My point here is, take a close-up look of the back of this Jimmy Foxx card.
The front of this card is perfect. That's not a "stain" in the lower left (it's part of the infield grass in the picture).
TED Z
T206 Reference
.