THX had a limited reissue in the wake of Star Wars’ success though.
Chewielewis, the copy that you saw in the cinema was this version that SilverWook says. This Warner logo was used between the years 1972-1984, what fits with the premieres of the original trilogy. The sky at the end is “clear”, not “dark” as in the 1971 version, with now, the Kinney Shield (used between 1970-1972). And this version also differs in the beginning: there is no Buck Rogers, instead a fragment of the movie Things to Come (1936).
No more changes in this 1977 version. If I’m wrong, that someone correct me.