The issue isn’t the age of the fingerprints, the issue is the age of the metadata from MusicBrainz. If you have a release that was added to MusicBrainz a year ago that never had AcoustIDs generated for it and you generated brand new AcoustID data for it now, it would all work correctly, because AcoustID already knows about the information in MusicBrainz. (AcoustID has a complete copy of the MusicBrainz database, including everything that isn’t associated with any AcoustID currently.)
What you describe perfectly fits into this: the release is new in MusicBrainz, so AcoustID doesn’t know about it currently/yet, because the replication seems to have currently stopped. So AcoustID either reports nothing or reports a different, “older” Release that it does know about.