I am a kneebiter (at least my kids are), and I can confirm what beewang said. The reason for my REALLY advance purchase is that I got the tickets to Munich using frequent flyer miles, and you have to get them way in advance in order to get the time and date you want.
Once I set the travel dates, I ordered my car through my dealer. I won't have the production number until January, which is when my date will be locked in. If you think about it, that makes sense. I am picking up in mid-May, which means that the car will have to be built by mid-April. Given three months lead time, that means mid-January for a production date.
Having said that, as beewang mentioned, I am penciled in on my target date with BMW ED. Given that I was the first one scheduled for that date, I am pretty confident that I will be just fine.
I'll send you a PM with my email address. Let's keep in touch as we plan our trips.