Yes 12 movies was mentioned on more than one occasion way back near the start of the phenomonen. I think the first mention was in a very early edition of Bantha Tracks the Fan Club newsletter. 12 movies didn't last for too long and got cut down to 9 fairly quickly.
In all fairness I also have an interview (in print, Rolling Stone I think) where Lucas says he is only planning 6 films and that was from the seventies, so we can't blame him for not delivering 9 movies.