Knight Rider had the covers from the word go. If they didn't, I would be surprised. I remember one episode had John Mellencamp's "The Authority Song" and it was a cover when it aired (I don't remember *exactly* what Mellencamp's name was at the time of release). So the fact that the DVDs have covers doesn't surprise me.
Universal did that a lot for all their shows including "Magnum, P.I."