Endless Summer Poster Collecting

There's so many Endless Summer posters for salein galleries, poster stores, the internetand okay how can a collector tell what's what?
Bruce Brown's The Endless Summer was first shown in 1964 with a 16mm film projector at local venues, high schools, halls and small theatres. Bruce Brown narrated and a musical soundtrack was provided by a reel-to-reel tape machine.
These personally narrated shows were prior to the nationwide theatre release in 1966 - 67.
Posters and hand bills were placed in surf shops, tacked on walls