I had a similar delay issue. Put my order in for sedan on Dec 28 with 19" rims. Had an original build week of week 6; then week 9.
During week 8 I called BMW and they had pushed me to week 15 (because of 19" wheel delay). Shortly thereafter, I was moved to week 14; and ended up being produced during week 13 (completed today).
I think its hard for them to predict build-weeks out that far...but also a pain in the ass that they can't plan better for supplies/parts. When was this company started? Last week?
Hang in there--chances are, they will move you back up again.