I've learned that people do not like to have their mistakes pointed out.
Therefore, in your position, you are better off to let the vet do as he wishes and not even bring it up, even though it is incorrect and not right for the game.
It is unfortunate, but people will hold a grudge against you for years for correcting them.
* I know the advice given in this post is downright cowardly, but sadly it's also true.
