It was on my original Darth Vader action figure from 1978 — "Darth Vader — Dark Lord of the Sith." I remember wondering, "What does THAT mean?" But the word wasn't used in any of the OT. It may have been in the novelizations, but I can't remember.

Fortunately, Disney has indirectly made clear that the prequels only constitute canon insofar as they can market them (and their toys) to children. Notice that the only direct prequel reference in TFA was the use of the word "Sith," which did not appear in any of the OT. It's so funny to see the prequel dorks try to…