It is probably bad UX to not make it clear that this is what's happening. But it would be much worse to fall back to a local business search, drop a pin on the result, and have the user think that it was an actual geocoder result.

Intersection searches are rare, and there's a limit to how large a set of queries you can have in a "the results of these searches can never change" golden set. Again, these kinds of things have always happened with map data, it's not some kind of new phenomenon. I'd bet there's no less QA going on than during the times when you thought the quality was good.