How do you determine value on this?

[Enfuego]

I agree with many of the previous comments. IMO, the stamp just adds character to the card, Don't sweat the fact that the card looks too good for the grade, collect just for YOUR standards.

[Leon]

I agree on the thoughts that errant writing and marks can add a lot of character to a card. My Buck Weaver 1911 Zeenut has a game scored on the back of it, I love it. Depending on the amount of paper loss, there is on the card, most collectors would take a mark or minor writing over the missing paper.....