I think season 6 or 7 (1974-1976). The earliest-known appearance of that sketch is a season 7 episode. The puppet in that one looks newer than the one in the "weather salesman" sketch, confirmed by Old School Vol. 2 to be from season 7. I figure the "weather salesman" sketch is the first where Grover comes to Kermit's home to sell him something, since it begins with Kermit telling Grover "I didn't know you were a door-to-door salesman". But then again, in the "earmuff salesman" Kermit makes a similar reaction ("don't tell me you're a salesman" -- and Grover makes the same "okay, I won't" response when Kermit makes a similar response to him being a plumber). Sometimes I wonder if that was done so it wouldn't be confusing in repeats (pretty much every season two pairing between Ernie and Sherlock Hemlock shows Sherlock introducing himself to Ernie). Then again, I do wonder if that "weather salesman" sketch was made earlier, even if it didn't air until season 7 (there are segments that didn't air the seasons they were made). Or, if they still used that older Kermit puppet in addition to a newer/better one, who's to say that they didn't continue using any two-collared Kermit puppets on Sesame Street after season 7 (when The Muppet Show began and Kermit stopped wearing the collar)? I mean, in 1979 they started using a different green material for Kermit, with less noticable texter, but there are some skits known to be from season 11 (Kermit News: Foot Snuggies, Disco Frog) that still used the more felt-textered Kermit.