The build week is from the dealer. The usual order is that the dealer’ll notify you that the factory has accepted your order and then at some point after that you’ll get a provisional build week (code 10) this can change so don’t take this as a definite build date, after that you’ll get a confirmed build week (code 20). When you get the confirmed build week it’s around 4-6 weeks after that for delivery to the dealer. All of these details are dependent on the dealer updating you regularly and likely take a couple or so weeks for the acceptance date.
I think 13 weeks is being optimistic but you never know.