I 'discovered' that 1964 Topps Giants Mantle variation (and others) in a thread here a couple of years ago. I remember thinking how bizarre it was that nobody noticed it before. The cropping of the picture is different in the two versions. And I agree with you, there's no way that line area accounts for the PD.
Edited to add: Found it:
http://www.net54baseball.com/showthread.php?t=218122