It seems to me that Nicholson and Muir were writers and producers at various points in time during the original run of "Howdy Doody," which was an in-house NBC production. One of their first projects as independent producers was a series of marionette interpretations of fairy tales with the puppeteers who'd worked on "Howdy Doody," sometime during the 60s (and I believe they were filmed in color, so they could pop up somewhere).
And speaking of Marilyn "Happy Harmony" Patch, there's a "WML?" from the early 60s where she appeared, younger and extremely cute, with an occupation of television children's show host. IIRC, it was on WHDH in Boston, then a CBS affiliate (of course, those who know such things know that the present has very little, if anything, with the old WHDH).
I tried to get info on what she has done since the "Howdy Doody" revival--all I could find is that she did a pilot for a kids series with some of the people who did "Howdy" after that show went bust. It didn't go anywhere. All I can assume that she's still alive, well and probably a grandmother by now.