Over the years, every once in a while, I've seen people say that the linking footage from the episode "Sing-Along" originated as an episode of the show. But now I've found this video of some of the street scenes, and it has the standard "Sesame Street was brought to you today by...." ending.
At first, I wondered if maybe it was a fan-made edit (after all, the audio could have come from any episode with those sponsors, the letters could have been photoshopped... but if it was an edit, the Sesame Street and Children's Television Workshop logos would have been really well-edited into the footage). Then I compared the end of it to the ending of the video, and this version has a little more footage at the very end that was not on the video (though the sponsor announcement drowns out Maria criticising Biff and Sully and Biff telling her he calls himself a republican). It's been a few years since I last watched Sing-Along, but I thought the last few seconds of footage looked longer than what's on the video.
It's a shame that we still don't know what episode number it is. It seems this was taken from an incomplete copy (which also seems to be missing the intro to "Doin' the Pigeon", unless that was an oversight by the uploader). I wonder what segments were in the episode version.
Another thing I wondered was if maybe it was produced as a home video first and then they re-used the linking footage for an actual episode. Not sure how likely that would have been, but it is an interesting thought.