For the "recording of work" relationship, there is no consensus on what "cover" means within MB, and no consistency in how it is applied. I think it has no value in MB unless/until it is defined.

Previous discussion @ http://musicbrainz.1054305.n4.nabble.com/Cover-relationship-Recording-Recording-tp3867677.html

Edit (jesus2099): fmera suggested to mark original recordings only, instead of all covers.

This idea has to be better defined but really is promising, IMO:

• Original is more easy to define
• No need to mark hundreds of covers (never ending job)