I think you make a questionable assumption, that "there is alread[y] a reservation number attached to each LEAF that will be manufactured..."
It would make more sense to give each customer a priority number. If the customer places an order within some set time (many reservation holders will not!) then that customer's car will be built in the order established by her/his priority. If the customer does not order within the time frame, she/he looses the place in line, and perhaps is dumped out of the early-order process. This way there are no "orphan cars." Your way, there could be as many orphan cars on dealer lots as early-order cars for early-order customers, and people willing to pay dealer mark-ups could have a Leaf before most of the people on this list.
Here's how I think it will work:
You get an opportunity to place an order based on when you reserved, with a large number of bugs in the system resulting in some people being able to order earlier, and others being pushed later. If you get your order in early enough, you'll keep your reservation-based priority, with a large number of bugs resulting in some people getting promoted or demoted in the priority list. If you complain, they'll make a half-hearted attempt to fix the bug, which might or might not be successful. When production begins, each car will be assigned to the next person on the priority list and configured accordingly, with a large number of bugs resulting in some people falling off the list and maybe a few people getting promoted up the list with no discernible system. If people walk away from the purchase, either the region will assign the car to a favored dealership, or the dealer may have the opportunity to choose to keep the car to sell or trade it to another dealer or return it to the region.
That's my guess.
Of course, it's also possible that just as certain regions get to order first, they make give production priority to certain sub-regions. E.g. they might build all Los Angeles cars before starting on the Seattle cars, and postpone all Spokane cars until after all coastal region cars, or some such arrangement.
We don't know because they've never said. This would violate the delivery-priority promises they've been making, but it would not surprise