If a Release that you know to exist doesn’t exist in MusicBrainz, please do add it:
https://musicbrainz.org/doc/How_to_Add_a_Release
Keep in mind that all information added in MusicBrainz is added by volunteers who donate their own time and effort into both populating and maintaining the data. If you find data missing or wanting in quality, the best way to remedy this is to add or improve the data yourself.