That skit also appeared in the season 6 premiere #666. Yep, they certainly didn't waste footage. I remember seeing "The King of Eight" in a season 35 episode, for real!
"The King of Eight" was one of only five "classic" segments shown in Season 35. The other four included:
- "The Magnificent Splasho"
- "Letter I (Beep Beep)"
- "The Letter P on an island to a rotating sunset" (but with the Joe Raposo music and original voiceover replaced by modern music and a new younger voiceover)
- and one other segment that I don't recall.
Season 36 had fewer classic segments from the 1970s. The only ones I know of are:
- "The Alligator King"
- "Consonant Sound - N for Nose" (with sound effects added)
- "Julius and Jasper vs. the apple" (the last animated segment from the 1970s ever shown on the series)
Season 37 had only one segment from the 1970s, and that was a Bert and Ernie sketch about Bernice playing checkers with Bert. The oldest animated segment aired that season was the "D/d (drums and drumsticks)" segment, which was known to have first appeared by April 1987.
Season 38 was when the show flipped the switch to HD format and segments from 1970s and much of the 1980s ceased to exist on the show by then, but did get released to Sesame Street's official website in the Classic Clips section. While the Classic Clips section is gone, some, not all, classic clips did get released to the show's official YouTube channel. I really hope more classic clips get uploaded soon, it is long overdue. At least the classic clips on YouTube proves that Sesame Workshop did not waste tape for sure.