That´s it. Mags and inserts are matched by the factory. Bodies and Mags on the other hand are not matched. It was quite common when buying a new Hasselblad kit back in the days that the body had been manufactured in let´s say 2002 and the mag in 2001 or 2003, according to the date code. Did not matter anyway. However, it would impair the sale value if you try to sell a 503CW with a mag from the 60s or 70s, just because it´s old and people pay premium for the newer gear.