Reversed back 1935 Diamond Star
 

Picked up these two Diamond Stars from a show table today from a large group of similar 30s singles. The dealer said they all came from one man's childhood collection.

Both cards look like normal low-grade cards from the front, but have reversed backs when turned over. I'm close to the complete DS set (missing two high numbers), but this is the first time I've seen a flipped-text back. Anyone else know what happened here? Is this a legit variation?

(Note that Bolton's top edge is displaced slightly, where it appears the paper slipped during or after being attached. The front itself is otherwise secure, no loose edges or curling.)