Steve
I don't have any answers to your questions, but with what we know now about the Mastro Wagner, it would be nice if the origins and details of what the sheet/strip/partial sheet looked like were revealed.
Ken
One player that stands out in my mind with fat top borders is Stephens St.Louis. I always take a second look at his cards.
Craig M
If you haven't already, add Wagner (left shoulder) SC 350-30 to your list of players with a factory 30 sheet number in the border.
Jantz