If it was registered in March then it might have an earlier build date. I'm not 100% sure about what changed around 03/07
If you punch the last 7 digits of your VIN into this website then it will give you your production date
http://www.bmwarchive.org/vin/bmw-vin-decoder.html
My production date was just over a month before the car was registered.
Where abouts in the country are you?