I think the print process can provide a ton of interesting fodder for historical purposes. There are some amazing threads here, on Blowout, or on PSA/CU boards like the BunchoBull 1990 Topps Frank Thomas NNOF thread.
https://forums.collectors.com/discus...n-to-my-theory
T206 fronts/backs/print process
O-Pee-Chee
There are some great threads about the history of hologram cards and the history of lenticular cards. There could be some about perforated (cut-out/fold-out) cards like Batter-Up over time.
Then there are items like the 1912 "proof sheet" that was just auctioned off for $40,000 that many believe is real and just as many believe is fantasy. Those are ripe for research projects.
Will enjoy seeing what you like and focus on.