a busy autumn
It's amazing what they accomplished between the test shows and the actual premiere.
The Gordon in the test shows (Robert Guillame) was replaced by Matt Robinson, who was on the staff as a writer, producer, and all-around helper.
I believe producer/director Jon Stone made the decision to integrate the Muppets into the street scenes rather than keep them separate. During the test screenings, the kids seemed to respond favorably to the Muppet and cartoon segments, but enthusiasm lagged during the Street scenes. So Ernie, Bert, and Kermit started showing up on the Street with the human cast.
To further integrate the Muppets with the humans, they took an idea of Jim Henson's for a big talking bird and thus Big Bird was born. J: im also took advantage of the opportunity to put some kind of Muppet "thing" in a trash can, and that's how Oscar came about. (According to Carroll Spinney, even before Oscar was orange, Jim came out with a prototype that was PURPLE!)
If some of these tweaks and twiddles weren't made, Sesame Street might not have gotten off the ground.