The title seems a bit confusing I bet. I have several albums with multiple artists on them. I prefer to keep all my album art in a separate folder (the only folder which allows for WPS album art is the \.rockbox\albumart folder). Since the name of the album art in this folder has to be artist-album.bmp it requires me to make a new image for every single track on the multiple artist albums. What I would like to suggest is to add a 7th priority check for album art: something with year and album name in it for the albumart folder.
Examples:
\.rockbox\albumart\1992-Sap.bmp
\.rockbox\albumart\Sap(1992).bmp
Also, how do you (personally you I mean) resolve album art for multiple disc albums? Do you just tag them all the same album and skip numbers for the tracks (e.g. 1,2...12.....(nothing)..(disc 2 tracks>>>).21, 22...32..(disc 3 tracks>>>)41,42...52) or do you just create 2 identical images with different names?