I do recall hearing on one of the DVD sets that the Butterfinger commercial was Milhouse’s true debut, and I do remember the commercial actually airing all those years ago.
But if was also shared at the time that Milhouse was designed for a completely different Matt Groening project, I did not retain that info.
In any case, Milhouse’s introduction in The Simpsons’ 1989 series premiere “Simpsons Roasting on an Open Fire” likely wasn’t the first time that Fox viewers had laid eyes on him, since he was hocking snacks to sweet-toothed kids a full year earlier, in 1988.