I’m new to contributing to MusicBrainz and I’m trying to figure out when it’s appropriate to use release relationships vs track relationships. It seems to me that people are somewhat inconsistent with this. For example, this page for Disco Volante by Mr. Bungle puts instrumental credits that apply to every track on the album in release credits and not in track credits (with instrumental credits that only apply to specific tracks appearing in track credits), but this page for Frances the Mute by The Mars Volta puts all instrumental credits regardless of whether they apply to every track on the album or just to specific tracks in track credits and not in release credits. I own both of these albums physically and the way these credits appear in the liner notes doesn’t seem meaningfully different from each other as far as I can tell. Is it redundant/poor form to put credits that apply to every track of a release in both release and track credits, or is that not really important? And are certain types of credits (i.e. instrumental credits vs. executive producer credits) more suited to one or the other?
The short version is that album credits should only go on the tracks (recordings) that actually apply. If you don’t know which tracks aren’t supposed to include some credits, they should go on the release-level, not all of the tracks (recordings).
Unless there’s track-specific numbers on these, both of these typically go on the release level.
I think of this as different levels of detail, and some editors like to focus on the fine details whereas some just want to get the data in (neither approach is incorrect, to be clear; I’ve been both editors, lol. I think it’s better to have less detailed data than to have none at all)
also seconding what @yindesu says above, tho I do want to add that I remember reading somewhere that executive producer specifically is generally added to the release and not the tracks. that said, that’s the only example that I can think of like that
also adding that for some credits, you can go by ear too, like if you hear a guitar on one track but not on others, or if you recognize a singer’s voice, or even if you hear that the guitar on a track is electric or acoustic. this might not apply to all credits, of course.
You still have to remember that many instruments you hear are not live instruments, but programmed. It’s common for soundtracks to use a mix of live instruments and programmed/synthesized instruments without clearly indicating which tracks use which. It’d be wrong to credit violinists, guitarists, drummers, for synthesized instruments.
@UltimateRiff’s comment is based on when you see a violinist credited for an album, and then you listen to the album and can work out which tracks they are playing on by hearing the violin on those specific recordings. Especially if there is no Keyboard\Synth player in the credits.
Best one is when you get a video of a gig. Makes it easier to confirm what is actually being played and by whom.
And my comment is about soundtracks (and other albums) where the release-level credits include both violinists and “all other instruments & programming” credits where you may not actually know which track goes with which.
It’s rarely the case that “synth player” is what we’re looking at when talking about programming credits.
yeah, like @IvanDobsky said, I’m mostly talking about what’s already credited in the booklet (or equivalent), tho that is good to note
With instrument credits, just do it as it’s actually shown on release.
The only time you should add any credit of that type to a track specifically is if the track number range is given right next to the credited performer, or if each track title has instruments and performers listed underneath it.
At times it may give number ranges for which tracks were done under a specific session, but even then it should go to the release level.
(This is one area that Discogs got right, for all its flaws.)
As far as executive producer. It can be a recording level credit, but I’d only do that if the booklet explicitly says it’s for that recording. Which I’ve had before, but rarely. It usually is a release level credit. But yeah, I usually only put credits on the recording level if they are shown that way in the booklet. I agree with your approach on performance credits.
The lazy man’s view: Loujine’s script to replace recording artists from performer relationships only works with Recording Relationships… 
True about the script, but that’s mostly for classical music - and in classical music, it is at least in 90% of the cases clear who performs what, except for maybe soloists in operas / oratorios 
For popular music, it’s often trickier.