You are correct in respect to the manufacturer's tolerance, particularly if you use the same brand of bearings you find in the gearbox.
But.
On the couple of functioning gearboxes I have pulled apart of other reasons (eg broken pawl spring, dropped oil channel etc) I reckon BMW (or Getrag) set them up on the tight side.
As I prefer to rebuild with semi-sealed bearings a re-shim is mandatory.
Cycle works is an excellent source of shims, much cheaper than BMW