Problem with characterizing these is that there are multiple variations in the Doby cards. Look at these three:
MIU, MIU+AEC, MIU w/AEC scratched out.
So there are at least four different versions of the card.
I don't think it would be out of line with expectations for there to be a slight difference in image size every year during a card's issue. The question is whether these variations are of academic or actual interest. IMO a true variation like the different legends on the four Doby cards is far more interesting than minute image size variations between cards within a specific type, but that's just me.