On the Sesame Street 2 album, you have:
Herbert Birdsfoot - High part
Ernie - Middle
Bert - Low part
One tiny bit of trivia that I observed on my own about the vinyl version. In the high part, HB doesn't repeat anything. In the middle part, Ernie repeats once, as in "I know, I know". But for the low part, Bert repeats at every opportunity. He says "Low part, low part", "I know I know", and "low low part". He even adds two extra "la la"s between the two stretches. The lyrics in the book reflected all this.
When they put them all together, everyone but HB said "agree, agree" (he said it once and sustained the "e" from the first). In the "la la"s, Bert alone added his extra two. At the end Bert and Ernie did four extra "la"s (not listed in the lyrics IIRC) while HB dragged out the last "la".
I used to wonder why they chose to have only the lower voices repeat (kind of a kid's view where everything has to be even or "fair"), but now I realize it added a varied effect to the song. The more of their music I hear, the more I realize that Raposo and Moss are/were musical geniuses.