It's possible. Frequencies are submitted to the database by users, so they are only as good as the users submitting them. That's one of the great things about RR, there's lots of information here, submitted by it's users. There are also some awfully knowledgeable people here, and not just limited to scanner technology, but all kinds of technical and occupational fields.
If you should happen across hidden frequencies, identify who/what it is, and once verified submit it to the database, the admins will take over and place it into the database tables.