Actually, they did show some pre-Kevin Clash Elmo after the recast. I know there's a late-1980s episode that contains "Me, Claudias", unaltered. Don't know of any other examples, though I'm guessing most of Meehl and Hunt's Elmo performances were in street scenes that weren't inserts.
Also, while it seems season 12 was primarily where Elmo spoke in grunts and single words, that season did show inserts where Elmo spoke normally, most of which I assume were made before they gave Elmo his name and early personality. Though I recently read that, while the 40th anniversary DVD lists it as being from season 11 (and it probably was produced for that season), "Me, Claudias" was first shown in a season 12 episode (after that personality was established in an episode).
And yet they still had no issue occasionally showing Green Grover up until the 80's, when he had a real jerky personality.
For years I would have thought they wouldn't continue showing those, but do know of some post-season one instances of the original Grover being shown, though most of them have Grover in minor supporting/background roles. Though I've heard that the first season "G for Grover" segment appeared at least twice in the second season (lately, I've been wondering if Grover might have been rebuilt as blue by then. Probably not, but I think he was blue by the time of the "What Kind of Fool am I?" sketch on The Ed Sullivan Show which came around the time the first season ended).
But I am surprised (more so than to hear they continued past season one) to hear they were still showing such segments during the 1980s. Though I'd be willing to bet that Baker #5 would be the most frequently-shown green Grover segment, though I clicked on pictures from the segment to see what wiki pages link there and only counted seven episodes (with the last one on the wiki being from the 1970s), and I wouldn't be surprised if maybe they cut that part in later airings (like how it was cut when Sesame Workshop first uploaded it online). But you never know. And if the segments have frequently aired in the international co-productions, then it might not be that odd they'd show them on the show for years after the color change.