You are all not thinking of this correctly.
You're all talking about this as if Tesla saves up changes for the "new model year". That's how other car companies do it--not Tesla. Tesla rolls in changes constantly in realtime when they feel like it and doesn't save them up. And this idea that you can get a "2021" version car in October or November doesn't happen. They switch over the model years on the cars coming off the production line sometime in the last few weeks of December, and the "2020" model year cars are completely identical to the "2021" model year cars that are made the next day.