That can't be Eve Plumb.....
That's Geri Reischl playing the role of Jan. She became known as the "fake Jan." Other than a ton of commercials she never did much else. She was cast for a role on Facts of Life but due to a contract dispute she was let go before production began.Eve agreed to do the first episode but would not commit to a reoccurring roll so the fake Jan was cast.
I just watched a few clips of the Brady Bunch hour on You Tube. Geri is very talented and better looking than Eve.