I wonder if the "Mr. Cunningham" comment to Mr. Hooper was a faulty memory too
I wonder if that was really on the show or if it's more of a funny anecdote that Caroll Spinney says in interviews, maybe as Big Bird. I first heard of such an instance in Sesame Street Unpaved when Big Bird was quoted as saying, paraphrased, "one time I walked in and said, 'hello, Mr. Cunningham!'... Gee, I wasn't even close." With that quote being him recounting the past, I would have expected that to be in an episode where they reminisce about Mr. Hooper, but I think the wiki has details on all such episodes (and we've had video of most of them for years) and it's not in any of those.
Regarding the Baby Monster clip: I wonder if we would have determined the case solved if we didn't know the segment was internally titled "Baby Monster: IS". He's not referred to by name, doesn't really look like a baby aside from being small (and arguably with him wanting to learn a word).
Regarding episode 1259: I wonder if the originally-scripted street scenes were shot and replaced. Has it ever been specifically stated that the unaired divorce episode is the only
episode/street story that never aired? I always assumed that, the A&E Biography says (and this is paraphrased from memory) "one episode went unaired", not "only one episode went unaired". If another episode or two was taped but unaired, they might just simplify the info as just one (if the quote was "one of two unaired episodes was about divorce", fans might be wondering about the other - though maybe not so much if they said "one of only a handful of episodes went unaired"). The idea of an unaired episode of divorce seems more likely for them to talk about than an episode that properly introduced a character who's not that well-known.