I was excited to see two of the earliest known uses of Elmo's name, and was surprised that he was referred to by name in season 11*.
The Muppet Wiki page actually notes Brian Meehl as Elmo's performer in the guide (in the scene rundown), I wonder if the script actually notes the performer (I know the scripts to sometimes note who plays who, does it do that with the Muppet characters?). I kinda thought Meehl would have started performing Elmo near the end of his time on the show, since I assumed that's why Richard Hunt took over and Meehl has said that he only remembers performing Elmo five or six times (of course Norman Stiles said that he only remembered Deena being in three or four scenes but we've found that she's been in quite a few more than just four, unless he was referring to the Deena and Pearl sketches and not street scenes; maybe he did perform the character a lot more than he remembers), and we know there are other instances in the early 1980s of other performers as the character (Jerry Nelson was Elmo in "Handful of Crumbs" which first aired in either season 13 or 14, and probably didn't have him mumbling there). But another appearance by this early incarnation of the character was posted, with Elmo learning the word "casa". I once e-mailed Brian Meehl, and he said that was the only specific scene with him as Elmo that he could remember.
*Based on the fact that he was identified by name in a season 12 press release talking about several new characters, by now I've learned that most of them actually did appear in season 11 or earlier, I knew a handful were around but figured they weren't counting them whether they were just extra utility characters before then or maybe just made one appearance before. In fact I figured Dr. Nobel Price might have just made one season 11 appearance, or maybe most of his season 11 appearances were in news flashes and season 12 brought him to the street, but I recently found on Muppet Wiki that the one Dr. Nobel Price segment that had been officially listed as being from season 11 actually made its first broadcast in season 12 (maybe it was produced for season 11 and held over a season?).