I believe doujin circles might be a similar concept to this
I feel like a series could work in some cases, but not all
a specific example I’ve got that feels similar is Dustcar Racing Syndicate
it’s made up of several people in a Discord server who generally make music under a time constraint (like a week), but they have released a couple charity albums featuring tracks from their members (with some collaboration, but generally no more than two or three people of the 15 or so that made it on the albums)
another example I’m quite familiar with is Pinkamena Party (most of this also applies to similar groups like Ponies at Dawn, A State of Sugar, and Equinity)
this is one of those examples where a series doesn’t quite work, since they’ve got a few, the mainline series, and each release usually has a spinoff release based on a holiday. (that said, there’s a few releases this doesn’t apply to, like Just Rocks or IT’S 2018 BPM, which aren’t spinoffs of mainline releases)
I forget if PP has public submissions or not, but I know some of these groups do allow absolutely anyone to submit tracks to be included on the album. some have online groups (forums, Discord servers, etc.) for members, some might not.
I feel like a new artist type would be useful, as it could be used to denote compilations (in the general sense, not the MusicBrainz definition, see here) released by a semi-consistent group of individual artists