I'm really thinking that a LOT of reservation holders were slow to order, or maybe even have not ordered. That was a big reason why reservations were opened up continuously faster with each group -- people were not placing orders initially due to lack of info. By the time they got to RN 10,000 or so, I think Tesla just said to heck with it and opened orders up to all US reservation holders. My RN was about 20,000. I placed my order on 1/12, after having access to the design studio for about 8 days, and confirmed on 1/19, VIN issued on 2/16. A colleague of mine was RN 66xx and he initially held off on his order until he could see the car, but then finally ordered about the time the Meet the X invites went out. He was issued his VIN yesterday for a P90D config identical to mine, but midnight silver with black seats and carbon fiber, otherwise identical.
I'm also thinking there are a heck of a lot more 90D's and even 70D's than P90D's...