There is a great video of an interview with the proponent of this and the interviewer tears the guy up
HERE. The error in the interview is the interviewer keeps saying that there are two components, the bullet and casing, which must be assembled and still match. He forgot the third component that must also match which is the box in which the rounds are contained.
So here we have a box which contains 20 rounds of ammo. That box is sitting on the line waiting for the 20 rounds to be marked, assembled, and then placed into that box. By law, the rounds must match with the number on the casing, bullet, and box yet there is no way to ascertain the match without actually opening the round; but to get back to the box.
If one of the rounds which is to be placed into that box is rejected due to some defect, the manufacturer must now also not only reject the other 19 rounds, which
would have been placed into that box; but they must also develop a method of that particular box not being serialized with the number of the rejected rounds so that ammo with the incorrect numbers does not get placed into that box.