What a difference a hair makes...
The 1971 Topps Greatest Moments #24 Bob Gibson is a tough card to find. No doubt about it. On the auction prices realized site, there are only 15 sales of any grade recorded since 2006. And of those, there are only four straight PSA 8's (the only PSA 8 I see on ebay right now is priced at $975 or BO).
Pictured here are three cards, with a pair of said 8's. Look how close to the border the top left-hand corners of the white boxes come. Very, very close. Now look at the PSA 8 OC. It is only but a hair closer to the border than the other two, a nearly indistinguishable difference and nothing to fret about. Here's the good news. The straight 8's both sold for over $400 apiece...but I was immediately able to (picture David Lee Roth) jump on the OC one the other night for less than a quarter of that price.