Jeff Ash was not the 20th person to figure out the date of the previous clip. He was actually the first of about nine people…
Probably the 20th person to weigh in on this bit of trivia, but I think this clip is from May 14, 1980. Don Adams had been married for 3 years, which he says on air. Per IMDb, it was the last of his 32 appearances on the show over 18 years.
IMDB says Adams married in 1947, 1960 and 1977…so yeah, that makes sense. It's interesting, if true, that this was his last time on with Johnny because as you can see, he did very well and Carson looks delighted with his performance. (Why it might not be true: I don't think IMDb has the complete listings of Carson's shows and their guest lists.)
But Johnny could be very mercurial about guests. Someone could be in favor and appear often with for years…and then one day, some little thing banned them from the king's presence. Wonder what happened here.