I have ripped a few home-made CD’s that contain a selection of, for example, world music. Some of these tracks are definitely in the Musicbrainz database (I checked!). Ripping software appears to look at some kind of CD-id and uses that for referencing, which does not work, since it is a selection of tracks that I have put on a CD myself. So, in the end I have a collection of tracks without ANY data. I can type over all tags, but being lazy I use the fingerprinting option. Currently I have changed the thresholds to zero (0) in Picard to get best matches. Some of the tracks return without result, although, as mentioned they are in the database.
In VLC when you have tracks in your playlist you can right-click to get a menu with options. One of them is “Information…”, open this and there you will find a button “fingerprint”. This often gives a correct match in cases where Picard did not.