Following a few e-mails, I just had a nice call from a lady at VW who is personally looking into things for me. Apparently they couldn't even get into their own systems this morning, but she will call me back later this week with some more details about my order. She backed up what others have said about the online tracker sometimes not showing until there is a confirmed build week, but to coin her phrase, "it's a bit flakey!"
I also got the contents of my entire order re-confirmed, because it turns out they made several errors when transposing the order information. While my telephone number, mobile number, and house number were correct on the order printout I got from the dealer, the numbers she had in her system were incorrect. Not sure why things needed inputting separately, but anyway, might be worth checking.