I wonder why they once mistaken the Up and Down song (Season 1 version) for being performed by two monsters, probably due to confusion with a
Sesame Street Book & Record recording that was later filmed with Cookie and Herry for Season 2. I remember reading the guide for Episode 0060 on Muppet Wiki, seeing it list Up and Down for being performed by two monsters. That sounds odd.

So apparently if the Silly Song Time segment "Up and Down" was in Episode 0060, how on Earth could a listing for "Two monsters singing 'Up and Down'" appear in the guide for said episode!!!??? I'm believing the listing of the two monsters' performance of the song in the Episode 0060 guide could be a documentation error (as stated above).