I used to have a lot of Super-8 digests of movies (Ken Films, Castle Films, etc) and I have a few items of memorabilia left.

One of the items that I have is a catalog for public institutions to rent movies to show; it is very interesting, especially the section that breaks down licensing fees and collecting entry fees. This specific catalog was printed in 1975 so you have to bear in mind that it is from before Star Wars and it is also before the ubiquity of home video product (Beta/VHS > LD > DVD/BLR).

However, despite its age, just about everything is in this catalog. Classics, new movies, foreign, there's no porn in it but they make it clear that some of the foreign films may have content not for kids. I suspect the 16mm print was struck for some entity like this.

When I was college in the mid-1980's our union had a film society and they showed movies in the union. Sometimes they procured older movies and sometimes we had films that were fairly contemporary. I saw a lot of movies this way because admission was often free or just a buck which is hard to beat when you are in college. Being a bit of a film geek/retarded development AV geek I can say that I would check out the projection equipment and I can say that sometimes we were watching pan and scan cuts of theatrical movies on 16 mm and sometimes it was 35 mm. I have no idea what was used for inflight movies on airlines in the 70's but I think that you may also have a candidate for your source there.