Welcome to Muppet Wiki!
I apologize for butting myself into this conversation, but I just want to say I really appreciate this newly-discovered information that I honestly would have never thought was true in terms of puppetry and voices (for instance, I did not think Paul Jacobs provided backing vocals in “Rock ‘N Roll Readers” - I was definitely certain that was Cerf. But alas, the ears can fool you. I also had a hunch Hunt was puppeteering Chrissy from the head bops).
Anyway, I hope it’s not too much trouble to ask - is this information only limited to songs from certain years or pretty much every song? Because there have been certain background characters I have been eager to know in terms of puppetry (The Moo Wave and Nickmatics for starters). Anyway, thank you for contributing this newly-discovered info! Can’t wait to see more!