Like David, Roosevelt Franklin and Uncle Wally, Willy the hot dog vendor is one character I am only familiar with through the internet, the Unpaved book &c. I know for a fact that David and Willy were around when I was of viewing age, but I just didn't remember or acknowledge either of them... after rediscovering this movie about a year ago, it was heartening to see Willy doing a bit of a cameo, even though he had no dialogue
ditto for Don't Eat The Pictures and Christmas Eve on Sesame Street for re-introducing me to David, and for giving another glimpse at Olivia and Mr Hooper (the latter two I always have remembered)