Posted By:
Tim NewcombSeries 19-24 cards never appear with any other back. I'm pretty categorical on that.
The 300 Subjects backs appear pretty often on Series 1 cards, Cobb, Wagner, CHance, BEnder, and the rest of them.
Once in a great while you'll see one from another low series, like the Byrne mentioned above, which is a card I have also seen. I have been charting these anomalous appearances as I could, and I've seen them in Series 1 and two or three others. Except for series 1, though, they are extremely scarce.
By the way, I've embarked on that Old Cardboard article on M116 again, and have hopes it will appear within months now (rather than years).
Tim