Most scopes with BDC reticles are made for an average. This would minimize the amount of discrepancy at varying altitudes.
For example, if you were at sea level and the reticle is calibrated for 16k feet, you will be way off....and vice versa. So to minimize this and to appeal to the broadest market, manufacturers have to compromise somewhere. This is why in the manual for each scope it still tells you that you must shoot it to verify.
One way to utlize a BDC reticle that doesn't match your loads is to tune your load to the reticle. Play with a ballistic calculator and find out what velocity at your altitude will get the closest to the calibration for your reticle. Then find the node your rifle likes closest to that velocity. Then of course, shoot to verify.
I can help with this and give you real world examples if you like. I have done this for two rifles with the Vortex BDC retcile.