Eh, the Sith weren’t really new when the PT came out. The novelizations and the EU had already prominently mentioned/featured them prior to TPM’s release.
I know the novelizations called Vader the “dark lord of the Sith”, but I think its current meaning wasn’t officially revealed until TPM.
Were they in the pre-PT EU too? I admit I don’t know much about the EU except for a few comics and videogames, so please tell more about it.