Here's my best guess as to why the orders are not actually being shipped in order the order was taken:
Anyone that has pre-ordered an iPhone in the past knows that the shipping notifications and tracking starts in China, not Louisville. My guess is that Apple made a deal with UPS this time around that UPS will decide who gets shipped the watches in each batch (but they probably have to stick to the order wave).
It's clear that UPS is deciding where the watches that arrive in these batches are going. They apparently are tied into the billing system so that when they scan a watch delivery Apple will charge the card and the ball starts rolling.
Now, as an example, lets say UPS gets a batch of 50,000 42 SG Black watches. They need to deliver 40,000 to Texas, which is the largest number for a state in that batch. UPS is taking 40,000 of those watches and shipping them to Texas. They'll find the next state that's closes to 10,000 (the remaining watches in that batch) and ship to that state. This would cut costs for UPS a lot! If it were truly in order the order was received, I'm sure that 50,000 batch would go to 50 states. That's at least 50 flights compared to just 2.
I could be completely wrong, obviously, but I bet that's what's happening and would explain why they are not being shipped in the order the orders were actually received. As long as they stay in the same "wave" of orders, it shouldn't cause too much of a difference and they save a lot of $$$ for shipping costs (Apple and UPS).
You could be on to something. Especially with how iPhones were always shipped. I can't remember how many times I received a tracking number for an iPhone preorder that said it was in Shenzen - or something like that.