It's extremely hit and miss. As far as VGA are concerned, dealers should not be taking deposits/signing contracts for cars not yet released. Thus, at least for all models released in the past two years, the customer specs for pre-deliveries have had zero relevance to the first shipment of cars, nor about whether you get a car in the first delivery or not. It's basically a situation of, if you've placed a deposit with a dealer, they'll probably give you first pick. But it's literally that, you have first pick of what they're given - which may be absolutely nothing like what you want. Sometimes the dealers can swap between them to make things better... but it seems just as many people end up walking away than compromising on their "order". And it's very rare that someone actually gets what they wanted...
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