I did a bit of searching on Google Books and there is an article from the June 28, 1972 issue of ComputerWorld that states "Ever since Hitachi introduce the Hitac 10 as a 'personal computer' in 1969, not only the regular computer manufacturers but electric appliance, calculator, watchmakers, communications and software companies, and even textile manufacturers, have plunged into the minigame." While they are talking about minis, what this does show is that the term "personal computer" was used prior to the advent of the Altair.