Upside-down Diamond Stars #37-48 card backs?

[Spike]

I've owned a #47 Cliff Bolton for some years with a flipped top-to-bottom back that looks authentic to my relatively experienced eye. It's low-grade and normal, other than the "upside-down" back relative to the normal front.

Not long ago, I spotted a second such upside-down back, #37 Urbanski, in a friend's collection. (#37 is a horizontal pose, so was trickier to notice right away.)

Based on both observed cards being in the #37-48 range, best guess is that some Diamond Stars sheets for that 12-player series were printed upside-down and made it into packs before being corrected. Anyone willing to check their sets or slabs for more examples? Those 12 numbers were only printed in 1935, a.k.a. green ink and 1934 stats in the bio. It'd be great to know if I'm on the right track to a simple explanation for the "flip."