Hi teknology
I think you have got hold of the wrong end of the stick there somewhere. The B3 stands for build number 3 with the B2 being the normal standard build 2 that is after the prototypes. The B3 was made especially noteworthy on the P67 boards with the problematic Cougar Point chipset that Intel had problems with. Hence the B3 revision was made public so that people knew the difference between boards that had been produced with the new improved chipset and the older troublesome board.
The B3 is just the build revision number.