There's actually something I'd like to point out. Yes, they do have some clips on there that are totally rare. Some may have only ever aired once or twice. But I think there are even some on there that have NEVER AIRED. Such as that one with Prairie talking about the word "Closed." But I think something is weird about it. Because there's a point where she says "closed" and looks at the bottom of the screen, AS IF the word "Closed" appears, but it doesn't. I'm guessing it was supposed to. I don't think it's been on American SS, but I have seen it on Plaza Sesamo, and the word "Cerrado" did appear there.
And there was this other one where Bert is supposed to shop for dinner, but Ernie locks him out of the apartment. At the VERY BEGINNING of the clip, you can hear the director shout "1, Action!"
And also, I noticed that a lot of these clips, like the one mentioned above, even include pre- and post-rolls that never aired originally.