It was in the books that accompanied their releases. And so was the name Palpatine. I have the original novel that came out sometime in 77 and in the prologue it talks about
Palpatine (by name) being the emperor and Sith Lord, so if you read that you already knew who the emperor was in TPM
I’ve had in my possession for years now a used copy of what I’m fairly certain is the very first printing of the Star Wars novelization and I’ve never gotten around to actually reading it. Is Palpatine actually referred to as a Sith? I thought that word was only used in reference to Darth Vader.