Clarifying Sith-y stuff (I hope)... Granted, this is almost entirely EU, and that's in abeyance until the Story Group finishes their winnowing. But I think only OT+ stuff is what's at most risk. Ancient past should be okay. Until it's not.
As far as being "Sith". Like the original Mandalorian species, the original Sith species is either extinct or nearly so. But thousands of years ago, the first Jedi Schism saw some Jedi "you can't fire me -- I quit!" from the Order for doing Unnatural Things™ and going into (self-imposed) exile. The ambivalence in my phrasing is due to how each side spins it. *heh* They eventually found their way past the Cauldron Nebula and happened upon the Sith, who had been living in relative isolation. The Sith species at least partially metabolized the Force -- drawing sustenance from it. The Fallen Jedi kinda moved in and took over and interbred with the Sith, and over centuries a more Force-capable hybrid subspecies arose as the ruling caste. These would be the original "Dark Lords of the Sith". Some still used lightsaber-based weapons. Most did not, using the Force in other ways.
Fast forward to Darth Bane's time. Several Sith Empires had pushed into the outer galaxy and been pushed back by the Republic. At least a couple times the Sith were thought to have been exterminated. But, as with the Mandalorians, it had become more a culture/philosophy than a genetic thing. So while there might be a few actual Sith out there by the time of the Great Galactic War of ~3600 BBY, it's mostly other species by then making up
that Sith Empire. And during all this time, there are many self-style Dark Lords of the Sith trying to claim supremacy and Bane got sick of that. The Rule of Two is that there is always a Master to wield power and an Apprentice to crave it... Two
Lords. Either or both can have many disciples or acolytes or apprentices of their own, but only one big-A Apprentice. They are
expected to scheme. And the various apprentices usually don't know the others exist.
George's (and Katie's) bad writing aside, the Force is basically like the Phoenix Force in Marvel Comics. A quasisentient (but not in a way we can really relate to) conceptualization of the life potential of the universe. Not infinite, but a lot, lot, lot bigger than we can wrap our heads around. Like a cell in our body trying to understand the whole -- only several orders of magnitude larger. Whether it's two Sith Lords drawing on that or two thousand, it's not gonna make much of a dent. The Rule was to keep the Order from destroying itself through internecine strife. None of those acolytes or apprentices are able to get anywhere near the power levels of the Master or Apprentice before they burn out, get killed, or get put down by the Master or Apprentice.
Also, letting Vader run around calling helmself the Dark Lord of the Sith (accurate, even if only the Apprentice) is a great way to draw attention away from the
true Dark Lord. A lot of people quibble over whether Vader's Sith or Dark/Fallen Jedi. I argue either could also be the other. Most true Sith Lords haven't bothered with lightsabers, so he's more Jedi-like in that regard, but that can easily be seen as an artifact of his early training. That's honestly one of the things that bugs me about ROTS -- Palpatine using a lightsaber. He made such a point in ROTJ describing it as the weapon of a Jedi, and being more interested in raw application of the Force, through lightning, through farsight, through mental manipulation, etc.
Anyway, on to the show discussion...
--Jonah