- Palpatine being definitely a Sith (as opposed to just a Dark Sorcerer)
Palpatine has been a Sith since TESB. Vader calls him his master in both TESB and ROTJ. He can’t be his master if he’s not even from the same Order. Vader has also always been a Sith since ANH’s first drafts.
Eh… the word ‘Sith’ is not mentioned onscreen til TPM (since it was cut from ANH - I think at one point Tagge or Motti said it?) and IIRC only Vader was called ‘Dark Lord of the Sith’ in public-facing materials of the time. GL had a lot of ideas and intentions, some of which are old and some which evolved over time. I’m going with what I feel would be cool.
‘Master’ could mean a lot of things. I think the most obvious interp is ‘master - apprentice,’ but that does not necessitate an institutional allegiance, more an expertise-sharing dynamic. It could also mean ‘master - servant,’ which is kinda suggested by some of Palpatine’s lines (“with each passing moment you make yourself more my servant”) - and Vader’s (“I must obey my master”).
Indeed. Besides, in both the Legends and Disney continuities, we have non-Sith darksiders who answer to Vader/Palpatine, even receiving training from them. The most notable example’s probably Mara Jade. And then there are all the inquisitors. So the notion that even masters/apprentices have to belong to the same order was never in play.
It’s probably difficult for some folks to wrap their heads around Vader being the Dark Lord of the Sith whilst being subservient to a non-Sith Palpatine because since 1999, the Sith have been portrayed as apex predators who have a monopoly on dark side mastery. But this is purely an invention of the prequels.