In Romania we have a rudimentary check in the {{Monument istoric}}
template - we check that the code begins with a valid county sign. If
it doesn't, we add the files to a special category. You could try
something like that, but that still means you'll have to fix them by
hand.

I second that. We’re also using that sort of template black magic in {{Mérimée}} for the French monuments.
It has proven very useful. − see <https://commons.wikimedia.org/wiki/Category:M%C3%A9rim%C3%A9e_maintenance>