Model Year Question.
 

Now as for what bmw does for model vs manufacture date Im not sure.

Easiest thing is to put the vin in a decoder and see what it spits out for the model year I would imagine.

Yes it is possible. I've seen BMWs manufactured as early as May that are of the following year's model year (say a 05/2012 manufacture date CAN be designated as a 2013 model if it was made to the spec of the 2013s).

On the same token, I've seen BMWs (albeit, older gens like late 90s and back) that don't show the next model year until later in the prior year (like Sep of the prior year). It really is a technicality as to the spec to which it was built to.

Absolutely and its the industry norm, usually most manufactures start model year production around June. You generally see them in the showrooms around September.
I know this for a fact as I spent years selling aftermarket auto parts where we had to know this information in order deliver the correct parts.

Its true, sometimes you get a weird one. I had a late model 08 that was badged a 3.0 x-drive and not a 3.0si. At the dealer, my SA also commented on how weird it was that it came up in the system as a 3.0X-Drive and not a 3.0si.

I was just talking to my wife about this kind of stuff today. My '98 E36 was built 9/15/97 so I was joking about how I'll be drinking a beer with it this year.

Her '08 X5 has a production date of 9/3/08 which seems mighty late in the year.

Ditto the replies above...build date and model year can be different. In the USA market...September is usually considered the "roll-out" month for the new model year...but due to circumstances...sometimes this time frame does not work.

The e39 had a June/1996 roll out date...and it debuted as a 1997 model year...and this was due to the US federal OBD II mandate which the e39 didn't meet the requirement for the usual September debut. Whereas the rest of the world got a 1996 e39...the US market didn't. The e39 debuted in the USA as a 1997 model...and the e34 5 series continued to get 1995 models through March/April 1996. So the US never had an official 1996 5 series model. :)

Also, the US DOT requires car manufactures to indicated the official model year designation in the 10th digit of the VIN (regardless of build date). See the chart below for how to tell the "official" model year of any car sold in the USA since 1981.

If the 10th VIN digit of the vehicle in question is a "D"...then it is a 2013 model year (regardless of the 2012 build date). If the 10th VIN digit is a "C"...then it is officially a 2012 model year: