I'm pretty sure the regional priorities will work like this because you can look at Tesla's delivery estimates and see how it works. In the screenshot, you can see that many Central or Eastern reservations show the same estimate as the earliest CA. As the reservation time increases, the estimate changes from Dec to Jan. That shows there is actually a calculation behind this and they are not just displaying the same thing to everybody.
I created the Estimator in September 2016 and there were no Tesla estimates at that time. Therefore at that time, my assumption was based on common sense. If you look at the message
here from October 2016, you can see that I was expecting 2 weeks gaps between regions. My idea was that it wouldn't make sense to overwhelm CA delivery centers with huge numbers while the rest of the US is not delivering any Model 3s. I thought a team from Tesla would travel from region to region and inspect every delivery center before giving the green light. That would take some time but not that much time.
Now I watch the invites to see how it works. Check out column C
here. I might need to change owner priorities. I assumed owners would have priority in their region once deliveries start there. However, it looks like Tesla is not waiting for that. They are shipping owner cars anywhere in the US now. Again look at column C on that spreadsheet. I think they are not waiting for delivery centers to be ready because owner cars can be delivered together with S/X anywhere in the US. The numbers are not that big. Only 7% of reservations are from existing owners.
You might say if owner priorities work differently, why didn't you change it until now? Because this is new. The data was added in the last 24 hours. A new batch of invites went out yesterday. Look at the dates in column H.