I’ve found evidence of the 12 movies bit.
https://youtu.be/AwWrMMBytZ4
Interesting video, though doesn’t it in fact confirm 13 movies, not 12? This advert from 1979 is speaking in the knowledge that Star Wars is already out two years beforehand and says “GL and 20TH CF have plans for twelve more block-busting chapters to the Star Wars story”.
It’s weird because I remember hearing over the years once the PT started that there were plans for 9 movies all up, then it was 12 and of course a couple of years before TFA, it was only ever meant to be 6 movies…yeah, sure George, whatever you say George…dickhead.
.Val