serial numbers
I would have to do some digging to find the exact rule number and wording...
but from the ABC rule book, and I would think it is the same elsewhere... if a serial number is no loger readable due to resurfacing (or in the case because of a weight hole), it is allowed to be RE-engraved on the ball....doesn't matter if it is the same numbers as the originals, just as long as there is a number on the ball before begining of competition, and that is the number recorded on the scorescheet (for the tourney if required, or the honor score award form when filled out after an honor score).
Hope that interpretation helps. I guess if in doubt, ask the TD's before the start of that individual cometition.