If I understand it correctly, the database is built from the *1 fid files, not the other way around. The database only uses the tags that it's hard-coded to use (Artist, Album, Year, etc.) and ignores any extra ones. The purpose of this (as I understand it) is so that as you up and downgrade to different versions of the player software without losing all of the *1 tag data. You can also create your own tag fields in emptool if you like (again, as I understand it).