- 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”).
If GL can get away w retconning Obi-Wan’s “master” to be Qui-Gon (as opposed to Yoda), I think I could get away w a similar stretch. I mean, I’m already doing away with the whole notion of a super organized Jedi Order & The Council. This seems small potatoes in comparison. At the same time, if Palp were a Sith I don’t think it’d change much in this outline - it’s just not necessary for him to be so, for this story to work.