According to the 40th anniversary book, Steve Whitmire's first performance as Ernie was in the sketch where Ernie and Bert go fishing, when Ernie keeps catching fish and Bert doesn't. That's the only instance I know of for sure where Steve performed Ernie in season 25.
According to the Muppet Central interview with Steve Whitmire, he said that he first did Ernie's voice when there was a need to make talking Ernie toys. I wonder what these toys are. Anybody know of any pre-1993 talking Ernie dolls voiced by Steve Whitmire? I actually started a thread about this long ago, and some people thought it might have been Sleep & Snore Ernie (which came out in 1997).
I wonder if maybe it took awhile for Steve to regularly do Ernie's voice. He hadn't been on Sesame Street until that point, and I think he was doing The Animal Show around the time he was recast as Ernie. Because there are a handful of productions from around the time he was recast when Ernie was silent (all of which have already been mentioned). Notice that Steve Whitmire has rarely performed anybody else on Sesame Street.
Though I know of a few Whitmire-as-Ernie skits that were broadcast in season 26 or 27, such as the one where Ernie does a drum experiment to see if Bert would fall asleep if he stood behind the drums without playing them. But I have a feeling he didn't start performing Ernie alot until season 29 or 30, performing on a much frequent basis until around season 36, when Ernie started making less appearances in puppet form.
I wonder if "A Musical Celebration" was recorded before Steve Whitmire's first Ernie performance. I read an article about Carlo Alban (the actor who played Carlo) which said that his first Sesame Street appearance was in that special, and I know he was on the show in season 25.
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