I used to think that George the Janitor was originated by either Jim Henson or Richard Hunt, due to him sounding different in The Muppet Christmas Carol and me knowing that Henson and Hunt were gone by then. And I was confused, because I figured Jim Henson performed Wally, and the Muppet Hits album listed Mildred as a Richard Hunt character (why wasn't George listed in the albums performers listing???), and I knew George was associated with both characters. Of course I didn't realise how it was done in At the Dance.
It is ironic because Frank oz still performed him (or at least the voice), despite using a different voice. I get the feeling that the script didn't specify who would say the line and Frank Oz recorded the line not knowing one of his former characters would be used. Heck, years later I incorrectly thought it was David Rudman doing the voice.
In A Muppet Family Christmas I thought that Richard Hunt was the photographer who took Miss Piggy's pictures. It sounded so much like Scooter. But Muppet Wiki says it was David Rudman (showing what a good choice he is for Scooter, though I feel the photographer sounded more like Scooter than Scooter has since Rudman took over).