I have a lot of works from old CDs.
There are no metadata written in tracks that are identified only Track 1, Track 2 ...
On the MacBook Pro (Sierra 10.12.3):
If I drag such a folder in the left window of MusicBrainz and I perform a scan, I get all the metadata in the right window. Wonderful!
On the iMac (Sierra 10.12.3):
The same operations do not give any results in the right window.
Same thing on a Mac Mini (Sierra 10.12.3).