The letterboxed one is probably from a trailer, which often ran with movies of a different aspect ratio. I used to see the projectionist physically flip the projector lens if a movie was a different aspect ratio from the trailers in the old days. Weird things would happen if they didn’t!
I’ve got some of those mounted frames, and a couple loose ones from a 70mm theatrical print, (which was turning red/pink) but I can’t recall if the soundtrack is visible on any of them. Will have to dig them out and see.
Interesting no frames from the Rogue One IMAX prints have turned up.
A nice gallery of scanned frames is here:
http://www.jedi1.net/