Hi,
only a car-manufacturer was able to homologate cars and parts. But this means not, that the parts have to be built by the car manufacturer.
By the way, BMW have done racing (with the 02) in the seventies, not circuit racing but rally! Think about the homologation of the M12 engine! The 2002 in season ´74 driven by Achim Warmbold and Jean Todt! Then the early years 70/71 Tony Fall/Mike Wood (BMW Works Car, Winner 2000ccm TouringCar Class TourAuto71) and Rauno Aaltonen/Paul Easter (the second works car) for example. So, you can´t say that BMW hadn´t done racing with 02 since ´69 ;-)
Cheers
W.
PS: many parts are not produced by Alpina or BMW! For example the Alpina rims. The rims were manufactured by Ronal not by Alpina. It is a long list, short steering: ZF, CR 5Speed: Getrag/ZF(S5-18), Frontstruts neg camber: Bilstein/Fichtel&Sachs, AluCalipers: ATE.......