I usually add relationship to recordings and works from Discogs, but they have some types of releationship that I cannot find on MusicBrainz.
Most of them are "contractor", "leader" and "toy", I have no idea what those are. There are also some types of relationship that have extra information on them that it's not possible to put it on MusicBrainz, so I don't know how to proceed. For example: "Recorded By [Additional Vocals]" (should I just put "recorded by"?), "Engineer [Vocals, Additional]" (there's no sub-category of engineer that describes this) and also "Producer [Vocals]" (what's the difference between vocals arranger and vocals producer?)
Sorry for the trouble.