Today is 12/17 and we have exactly 2 weeks to EOY. Tesla already has fixed build plan for 2 weeks and orders from CA made between October and early December. There will be no reason to assign VIN and delivery dates if Tesla is able to fulfill all the orders in 2 weeks. I strongly think, Tesla knows that they cannot build enough cars to fulfill all the CA orders so that they are trying to find how many orders will be cancelled and/or not take delivery by EOY. Once they get the numbers, they will give opportunities of taking leftovers to November orders.
That is why Tesla is sending an email to know unavailable dates for delivery to customers made order in October. I think Tesla will send the same email to November orders beginning of next week. So, it is all depends on your luck to get delivery by EOY.