After the talk about Guy Smiley’s few appearances in the early years, I decided to check, and it looks to me like Guy Smiley made an average of five appearances or less per season when Jim Henson was performing him. Of course this does not count segments where he’s mainly just in the background, or unnamed appearances in the first season (I think I’ll count the two game show segments where he has other names).
Some segment characters seem to have had the majority of their segments debut on their first seasons. Season two has the highest amount of Sherlock Hemlock segments, with following seasons having very few new appearances by him (I also saw that the majority of 1970s Sherlock segments were last aired around season 16, while the later Mysterious Theater segments aired quite a bit in the 1990s).
I think most Amazing Mumford insert segments debuted in season 3, though he would go on to be seen in street scenes a lot over the years.
Most Lefty the Salesman segments debuted in the first three seasons, with few new appearances afterwards. Many of them continued to air until season 29, though I think a lot of them were last seen much sooner (I think the notepad salesman and ME salesman bits weren’t shown much after season two).
I would have thought most of the Little Jerry and the Monotones segments aired in season 3, but I don’t think there were any seasons with a ton of segments with them. The first two seasons had many precursors to the characters, some arguably them (I consider Mad and maybe The Word to be their only real appearances in season two, though I will also count them as being in Grover’s walk and exit bits). I thought Proud debuted in season three but I think the wiki notes it as debuting in season four, I can’t remember of Sad debuted in season 4 or 5, I think both Danger and Telephone Rock debuted in season 6, and other appearances were scattered over the years, very few and far between (it kinda feels random that they would suddenly come to the street in season 19, then have an episode where Elmo has to fill in for Little Jerry in season 22, and then make an appearance on the street in season 31).
Most of Herbert Birdsfoot’s appearances were in season two, which I am not surprised by. I used to think that he was only around in new material that season (not counting a background appearance at Ernie’s surprise party for Bert), so I am more surprised that a handful of his segments debuted after season two.
Another of those odd things is how the early Alphabet Chat segments debuted in the 1970s, then we got a couple more in the 1990s. By then they stopped airing the former ones (most likely due to the pipe, which seems to be him actually smoking, in constraint to Alistair Cookie having a pipe to look classy and eat). But then they only did two new Alphabet Chat segments in the 1990s, in addition to giving Mr. Chatterly a street appearance.