Interesting list. I share you lack of interest in most of the items on your list (WC, locandinas, daybills, Japanese, Yugoslavian and Russian posters), but I do collect the occasional French small poster when the art differs from the large format (as is the case with those great early Hammer posters designed by Guy Gerard Noel for example). I also try to focus exclusively on movies that I have seen, but I make the occasional exception to that rule (in which case I try my best to track down said movie after purchasing the poster). I share your distaste of linenbacked posters, apart from the occasional slip for a large format when a folded copy is hard to find. I also don't care for inserts (that format is too damn narrow and seem anti-cinematic to me, lol!) and I don't collect any Swedish or Polish paper.
I'm surprised you've seen few movies prior to 1940, as a lot of them are easily available these days, and there are some truly great ones: the first batch of Uni horror obviously, but also the Pre-Code era and the great screwball comedies of the 1930s to name a few. You're missing out on some classic, man!
