I've noticed in the last few weeks that it seems an English copy of Don't Throw That Trash on the Ground is no longer online, and it seems like it might be blocked. A link to the video was in Toughpigs' season 21 article from the Sesame Street 50 years article series, and clicking on it says that it was taken down by Sesame Workshop. Too bad this hasn't been released commercially (I searched and it looks like it's not even on the Sesame Street video site anymore as well).
Some time ago on the Toughpigs forum, Scott said that something he uploaded on YouTube was taken down by Sesame Workshop even though it hadn't been released commercially (I don't think he said what clip it was), and speculated that Sesame Workshop might be doing content ID matches to prepare for when the classic episodes come to HBO Max. Maybe this is the case. I saw that post a few months ago, and if that is indeed the case and some clips can no longer be seen on YouTube as a result, then it's amazing that I've only been unable to find one particular clip I've been looking for. I have pretty much been able to view any other Sesame Street clip I search for online that had already been online for some time.
Then again, there have been periods when several clips are temporarily blocked/taken down by a third party, I want to say there might have been another period when Sesame Workshop took down certain clips that eventually came back but I'm not sure. In fact I recall that several fans here have mentioned that they deleted their YouTube channels just because of newer regulations, and I'm not too sure off-hand what clips they uploaded - so it is impressive that I can still find practically any clip I want that has been online for some time.