Yes that's one of the problems with the theory. No cards with guidelines.
It may be just possible that cards could have been cut so that the guidelines always got removed.
One of the things I want to do is to make some measurements of the scan to see if this just might be possible.
Ted has already put a fine cap on any thought of the AB cards being made consecutively. They definetly weren't, so the idea of them being made on a particular set of cutters that was only used for a certain time is out. And a different machine that was only used for AB cards makes so little sense it's probably out as well.(And still leaves a nearly unanswerable "why")
I don't recall seeing any cards cut offcenter side to side enough to show the next card, although I've got this nagging feeling I'm wrong on that.
I know enough printing to get myself into this sort of trouble.
A couple years in a shop that cross trained everyone. So I've actually run many of the small production machines. Plus I studied CAD/CAM, and did 11 years of industrial machinery repair.
Everything is the way it is because of how it's made. Make it differently, and the end result will be different in some way.
Steve B