Rule of Two?
Is it me or do the Sith in the first 6 films not really bother with the Rule of Two?
Based on the pre Force Awakens canon:
During the events of the Phantom Menace, Plagueis was Sidious' master and Maul was Sidious' apprentice. Sidious apparently killed Plagueis while Padme returned to Naboo. Unexpectedly, Maul was defeated and thought dead, meaning the number of Sith went from 3 to 1.
Sidious took on Dooku as his apprentice so they were back up to 2. But then Dooku took on Ventress as his apprentice and also taught at least something of the Jedi arts to Grievous. So arguably there were 3 or 4 Sith present right then.
Dooku gets rid of Ventress on Sidious' order so they're back to 2 (or 3 if Grievous counts). But Dooku seemed to believe Anakin would be joining them too making it 3 or 4 (of course Sidious intended for Anakin to replace Dooku rather than join him).
So when Anakin kills Dooku, he doesn't join Sidious immediately so the number of Sith is down to 1 or 2 (Grievous' status becomes even harder to grasp with his master now dead. Obi-Wan kills Grievous so that gets rid of that particular question mark. And then Anakin joins Sidious as Darth Vader. So we're back at 2.
Of course then Vader takes a secret apprentice in Starkiller. So this arguably makes it 3. Except Starkiller was never a real apprentice, Vader was using him to lure the Rebellion into a trap where he would kill them all and Starkiller. So it's safe to say the Rule of Two was actually being followed here.
Then Luke comes into it and it all gets very confusing. Sidious gives Vader blessing to recruit Luke to the dark side. But surely he would not intend to be overthrown nor would he expect Vader to just step aside. So it seems Sidious was at least on the surface condoning there being 3 Sith.
Vader offers Luke the opportunity to overthrow the emperor and rule together which would make it 2. But did he actually intend this or was it merely a way to lure Luke to the dark? In which case he's still going for 3 as Sidious seemed to want.
In Return of the Jedi, Vader has abandoned any attempt to get Luke to help him overthrow Sidious. Presumably he therefore thinks Sidious wishes Luke to join them rather than replace him. Sidious seems to go along with this at first but when Luke defeats Vader he offers him the opportunity to take Vader's place at his side. So was Sidious always intending this or was it a last minute change in strategy when he recognises just how strong Luke is?