At the time TNG's casting was first announced, I knew Burton from Roots and I recognized Frakes's name from the miniseries North and South, in which he played a major role. (Although I think I mainly noticed his name due to its similarity to the author of the source novel, John Jakes.) I knew Brent Spiner from his recurring role of Bob Wheeler on Night Court -- particularly since Bob was set up in the finale of the '86-'87 season to play an increasingly prominent role (he bought the newsstand in the dining area), but then vanished without in-story explanation at the start of the '87-'88 season.
I know that Michael Dorn had a recurring role on CHiPs before TNG, but I don't think I watched that show much.
I know that Michael Dorn had a recurring role on CHiPs before TNG, but I don't think I watched that show much.