I think this was done by coinop when selling the carts because they didn't want to be tracked by the serial number
So "The Man" can't trace you.
Yep, that the reason why Serial Numbers are missing from many carts.
Not even talking about MVS carts, removing serial numbers was common in the late 80s and 90s for many products.
People who didn't want the item to be traced, nervous about Big brother, or just taking there view/practice of the
First Sales Doctrine to the extreme.
I remember doing this to my stuff in the 90s, Movies, video games, computer parts. People did it on everything except automobiles and guns (as that is illegal).