Posted By:
Anthony S.Here's a previous discussion on this issue. Essentially, there's a narrow size range in which the vast majority of T206's fall. They're not all exactly the same size. A slightly oversized card may appeal to some collectors, and suggests that it is much less likely that it was ever trimmed (although card doctors would prefer to start with oversized cards for obvious reasons). Doesn't really affect the value unless you have two or more collectors with a predilection for oversized cards who are bidding on the same auction.
http://www.network54.com/Forum/153652/message/1090717955/last-1090718359/T206+sizes