I consider different stocks to be a variation, and so this isn't a RPD for me, but I think many of you guys are doing RPD's and not doing stock variations. You pick if this counts
I think every white back card of Alston has this frame gap in the top left, and all the cream back cards don't have the gap. The cream back is a little easier in series 1 but the white back/frame gap card isn't difficult at all. I'm pretty sure this is a clue to which stock was the initial run, I have most of series 1 with both backs but haven't finished hunting down all the RPD's with both backs and observed enough to know if they probably don't exist with a certain back. I do think Alston here implies that the two stocks were not done at the same time.