I spoke to a Tesla rep about this and the official line is that when an order is placed, it acts as guide for the factory. The configurations are limited in scope, so when configured for RHD vehicles a block of RED, LR, WHITE INT cars will be produced when it's logical to do. Some can uncannily clip an immediate production so actually allocated a car sooner, some just miss the slot so fall on a later ETA date. Mass produced WHITE / MSM / BLACK are being churned out frequently, but waiting list is longer, you get allocated when you reach the front of the queue.
I don't think there's any RNG, but it is a fun suggestion
The best way to get a car without waiting in line is to mash the refresh on Tesla inventory when a boat arrives. Any orphaned cars will go straight on inventory, and that inventory is used by Tesla AND quick fingered prospective owners happy to negotiate on spec and immediately snatch a car.
For newer members to the forum, the UK inventory link is
HERE - all the filters can be set from the left panel and you can set up tracker alerts as well.
Happy hunting!