Regarding Lucas swearing up and down that he had always planned on stopping at 6 movies:
I have this vague recollection of something I read, back in 1977 or 1978, that had him projecting a dozen movies. Then, around 1980, I distinctly recall reading that he was talking 9 films. I don't believe he started swearing up and down that he'd only planned on 6 until well after RotJ was released, maybe not until he started working on TPM.
Not sure whether it was a case of diminishing expectations ("The Pyramids of Egypt were originally supposed to be big cubes"), or of using up his story material faster than he'd originally planned.
And yes, Palpatine was given as the Emperor's name in the prologue of the ANH novelization. Although that same prologue also had him ultimately becoming a puppet of his own advisers ("boot-lickers" was the term ADF used, as I recall), rather than being a Sith Lord. Although knowing his devious ways, Palpatine may very well have deliberately led his boot-lickers to believe
he was their puppet, when it was to his advantage to do so.