I'm still working on our article...
Here's what I've found on MC so far:
Mikealan: “Season Five Premiere (#536)-Fat Cat by Mahna Mahna-D and 2”
I have the Muppet Show version of Mahna Mahna on the Juiet Prowse episode of The Muppet Show on Time-Life Muppet Show video volume number 15. I, of course, have the original Sesame Street version of Mahna Mahna from 1969 on the Rainstorm episode from 1972 of Sesame Street Unpaved.
The different Mahna Mahna on Sesame Street wears sunglasses and sings Everybody's Song and Scratch My Back. I have the Scratch My Back song with Mahna Mahna on tape that has parts of the 1987-88 season of SS ("My first Sesame Street").
I surely do remember seeing the other different Mahna Mahna singing Fat Cat Sat Hat on Sesame Street Unpaved-episode #536 at the Museum of Television & Radio, too!
and
Mahna Mahna, who appeared on The Ed Sullivan Show in 1970.
Danny Horn, Toughpigs.com
and
Phillip Chapman noted:
Mahna Mahna first appeared on the Ed Sullivan Show in 1968, Sesame in 1969, then the Muppet Show in 1976.
So, was the Ed Sullivan show appearance in 1970 or 1968.