One classic instance (even though it was not related to censorship or legal issues) was the Star Trek episode “The Cage”(the one with Captain Pike and rejected because it was too cerebral and too good for TV). Gene Roddenberry thought he had at least two original full colour and original sound and dialogue prints of that episode and as it turned out the one he gave to have chopped up and glued into the TOS two parter “The Menagerie” was the only one he actually had (though he had a black and white rough cut he showed at conventions).
And it was not until the mid to late 1980s that a colour negative of “The Cage” was discovered in Paramount Pictures’ archives (along with the master tapes of Alexander Courage’s original soundtrack music), so we could see original colour footage of scenes deleted to make room for “The Menagerie” scenes. One main thing missing was original dialogue sound from Malachi Throne playing the original voice of the Talosian Keeper, as Malachi’s voice was removed because of his playing Commodore Menendez in “The Menagerie” and Vic Perrin’s was used (with the voice pitch altered) in the version(s) we are familiar with today. And it would have been nice for that to have been restored in recent years as Malachi only passed away a few years ago and maybe his voice could have been added back to a more original recut of that episode.
Wow! Thanks for that tidbit of trivia. Now I can impress my Trekky friends with somee thing they may not know!............