JQL to find issues that have exactly only one fixVersion

Currently, if an issue has multiple fixVersions set, a JQL like:

fixVersion = "1"

will return all issues that have a fixVersion set to 1, including issues that have multiple fixVersions. To further narrow down the search results you need to use NOT IN. However each time a new sprint or nested version is created, we now need to update our filter to exclude the new nested version. It would be nice if there were a "matches EXACTLY and ONLY this" function/command.