OK if “Prefer local metadata” is turned on, your embedded meta tags better be immaculate and complete.
And your folder organization better follows the rules laid out below:
Your example album
I have this in my “Greg Lake” folder, because he is the album artist, but some of the tracks are from ELP or King Crimson
should be fine where it is, as long as every track within this album has an “Album Artist” meta tag which has “Greg Lake” as content. The actual performer of the song should be in the regular “Artist” meta tag.
As for your soundtracks and samplers:
The folder hierarchy of
Music / AlbumArtist / AlbumTitle / Tracks
applies to samplers and soundtracks as well.
Which means that you cannot store albums which differ in their album artist inside the same artist folder. Otherwise you’ll see the exact issue you have now, where the album artist of all albums inside will be overridden by one of the albums.
So, if you have e.g. the Rocky Horror Picture Show soundtrack, you cannot store the album inside of Music / Soundtracks / Rocky Horror Picture Show OST,
because the album artist of that album is usually tagged as “Richard O’Brien”. So it belongs into Music / Richard O'Brien / Rocky Horror Picture Show OST.
Which in turn means that all tracks of all albums which are stored inside of
Music / Various Artists / must be tagged with “Various Artists” as their AlbumArtist.
Which in turn means that you better don’t use a folder like
Music / Soundtracks / if there is even one album inside this folder which has a different AlbumArtist than the rest of them.
