Posted By:
Anthony S.I may well have the exact reason wrong, but I did find the link I was thinking of. As always Ted provides some interesting insights into the T206 set.
edited to add: It was the Green Cobb with Piedmont 150 back which Ted specifically cited as often being miscut with wide bottom borders and short top borders. The card Marty linked to start this thread is a Piedmont 150 back.
http://www.network54.com/Forum/153652/message/1196605872/Those+darn+cards%2C+consistently+O-C%2C+what%27s+yours>+-