Responding to this post has been on my to-do list. Sorry it's taken me so long to get to it.
I'll be getting and reading the book in the near future.
A couple of scenes of the second pilot were filmed on a Saturday when I happened to be in Los Angeles (for another reason). Only Jim and Johnny were in the scenes, but Kaley was on the set and introduced to the audience. I don't think Simon and Kunal had been cast yet.
I got to see the show being filmed one more time (before its popularity skyrocketed) and was able to offer a storyline suggestion to Bill Prady; I could tell that he thought it had merit. I was thrilled later on that season to see my idea used in a storyline.
Despite knowing someone who knew the science advisor on the show, I couldn't get in to see another taping.
Unlike Young Sheldon, the show held up for all 12 of its seasons.