Sometimes liner notes are very vague and not specify which artist performed which instrument on which track. Should those relationships be placed on release or recording?
When they get vague like that, I usually put it on the release. But that is usually a case of all the notes are ambiguous.
Same as @CyberSkull, when it is not clear enough that the relationship applies this or that or to all recordings, we should set it on release level.
Release‐artist relationships mean « somewhere in the release ».
Specific per recording and general per release performer, etc. credits
On the release unless you know from other source which recordings they apply to. See http://musicbrainz.org/doc/Style/Relationships#Crediting_an_artist.27s_role_at_the_track_vs._the_release_level
Thank you for the clarification.