Like Crow said, stills with no NSS info came directly from the studios usually in presskits. At one time the studios would issue stills like this with press info throughout the production of a film. The presskit as we know it, containing stills & press info in a custom folder didn't become the norm until the mid 70's.
NSS would send black and white still sets to theatres, usually in paper bags stamped with the films title and number of stills inside. For reissues, NSS would just restrike the stills with a new NSS number on them (R-74, for example). For really big films (Star Wars) NSS would reduce the number of stills in the set the later the film played. The very first sets had, I think, 35 stills but by later in the year the number was reduced to about 10 or 15.
The color 8x10 sets were only made for specific films and usually were in sets of 12. By the late 60's they were generally just a set of 8, using the same scenes in the 11x14 set. But there were exceptions to this rule, too.