Even more bizarre was the showing of David clips from the 70s, and the next day a "new" segment of him would appear, really showing such a drastic difference in appearance
Speaking of which, I always assumed that the segment with David roller skating in Central Park was taped in the late-1970s, and when I saw a version that had modern wrap-arounds presenting it as fantasy, I thought they just shot those so they could continue airing it when David looked a lot different - only to be surprised that it all debuted in season 12. I felt he looked more like his 1970s self in the flashback and his 1980s self in the wrap-arounds (maybe it was shot earlier and held over until he looked more different so they shot some wrap-arounds).
Anyway, the wiki now has a guide for an interesting episode with an adult character believing in Snuffy (even though she doesn't see him):
https://muppet.fandom.com/wiki/Episode_0965
And from what I've heard in discussion/on the Snuffleupagus page, Big Bird informs her of his music entrance and she hears it. Perhaps Big Bird should have told the others about the musical cue so they'd know to show up and see him. Might have been more effective than a secret word.