This is the recent Tesla process. You place an order and they try to find one already built or coming down the line to get you one quick. If your exact configuration is not available, they will see what is close and offer it to you for quicker delivery.
If nothing pops up, they will need to wait until the factory gets around to producing your car, and there are lots of variables that can delay or speed up its arrival.
Tesla put on a huge push to get as many North American orders delivered as possible by end of Quarter (September). Were even giving cusomers free upgrades in wheels or colors if necessary to get the delivery done. Now they have shifted to huge backlogs of orders in Asia and Europe. They will be shipping pretty much everything they have overseas to deal with the long shipping times and the many eager customers with deposits.
So, buying a Tesla involves some planning and luck. Even the delivery specialists do not know all the details. They just have fresh sheets of inventory numbers available to them, and work their butts off trying to match customers with production/inventory.
If you are not flexible, and have a hard point, like financing, insurance, selling your current car, lease coming up, it gets really hard to pin down a hard delivery date. Delivery specialists work hard, but are always constrained by reality.
I waited 1 1/2 years to get my Model X. Thought I might never get it...then BOOM...there it is.