In many place in CB we explicitly handle the case where there might be a review for an entity id that no longer exists in MusicBrainz, however this has a habit of causing weird interactions in the interface (CB-367, CB-401).

I wonder if it's worth the effort to handle this situation, given that it probably happens very rarely. It's possible that there is a case where we have reviews for things that were never in MB that I don't know about? In any case, I think that this situation happens so rarely that we could probably remove the functionality and deal with any instances of it on a case-by-case basis.

The last time we encountered a bug because of this issue was when a spammer created a release in MB and reviewed it and the release was subsequently deleted.