Sith was never said in the OT…
Actually, there is a deleted scene from the conference room where a Sith Lord is mentioned:
https://www.youtube.com/watch?v=8Erf6s_wYJk
Yeah, I’ve seen that clip. Good stuff, should’ve been in the film.
It’s unlikely the internet nerds of 1977 were able to pass the clip around, though…so “Sith” was still definitely unknown to the majority of the world until Phantom.