I love Alistair Cookie with a pipe.
I'd say Sherlock is closer to a Guy Smiley/Herry/Mumford character than Harvey/Don Music/Lefty... I thought it was odd when they grouped him with the other obscure characters in the 50th celebration. When I was younger I had a computer game where he was the main character and it seemed like he was decently regular on the show until the mid-'90s.
As Oscar said, we typically associate dead Muppets with having a reason for being phased out, but Sherlock really doesn't have that.
As I said above, all things but the two big episodes were abridged.
Looking at the guide, there was an 847 scene omitted of Margaret Hamilton filling Hooper's with brooms between her getting her broom back and leaving. I noticed they didn't show any of her scenes that could be deemed "scary"... maybe they were bracing for leaks. I mean, most of what they showed was just the mellow part of the episode with her being a sweet old lady.
So while they showed 847, they really didn't show the reasons it was banned imo (aside from maybe a few cackles outside of Oscar's can). I'd compare her manic appearance as the witch to Pennywise the Clown in that I agree with Sesame Workshop for having absolutely no desire to release the episode.
From what I gather, the whole episode gives off more of a vibe of a movie or special than an actual educational Sesame Street episode... it doesn't even feel like a SS episode in some ways.