Probably very closely related to what the options on the car were, so you need that info too. On E46's, transmission choice, folding seats, and even which stereo influenced which spring paint marks the cars had.
My 2008 E90 M3 has X1 front springs, I will look at the rears when I get a chance. The only factory options were 19" wheels, cold weather, and premium packages. A car equipped with the sunroof, DCT, and tech package would weigh in excess of 90lbs more than my car, so I think it's safe to assume it would have different spring codes.