Roly Poly added in the Black Hood story into the middle of their book. So, it's not likely that these were already bound insides. It's a lot more likely that Green got ahold of the MLJ plates or original art in a warehouse sale, or a special deal with MLJ, who had already changed Top-Notch Laugh to Laugh Comics, and their book's features had mostly changed to other (new) features with new lead characters.
Link to the book:
Roly-Poly Comics 12