Pendatically speaking, people do get credit for fixing problems that never happened.

E.g. if the problems are quantifiable and there's a record, like dropping homicides from 100 per year to 20 per year in a city. Those extra homicides "didn't happen", but the improvement is understood.

For an one-off problem, it depends on how clear the path to the problem is. An electrician doing an inspection and noticing and fixing big electrical issues in the installation, would be appreciated, even if the accidents didn't happen.