I just noticed that the song "Street Garden Cooperation" made its first appearance in episode 1956 (season 15), and I used to think it was from season 16. There reason I'm bringing this up is because on the song page, Kevin Clash is listed as one of the performers, and I know season 16 was his first season of Sesame Street. Should we actually take Kevin's name out if he's not in it? I'd like to know what's up with that.
Clash had sometimes performed before season 16. We know that he performed a number of roles in season 12, and his voice is heard as one of the Anything Muppets in this number. Don't really know what the deal was, his autobiography says that he sometimes for to visit the studio (thanks to his association with Kermit Love, I think) and lend a hand.
I took Clash out, at least for now. I don't think we can positively confirm it was him based on a few 'dig it's. The contract story does bring into question whether he actually performed during the season at all, even though he was signed, apparently.