I stand corrected. I just did some research, and the syndicated Jeopardy of 1974 ran concurrent with, not after, the last season on NBC, and was a weekly show.
The 1978 version was, in fact, on NBC, and it was NBC who demanded all the changes in the format in that version. When Merv brought it back through King World in 1984, he made sure the game went back to the way it had been played in the 1960's.