Can you send a sample of two songs from that album to email@example.com
so that I can look at the tag information and determine the best way to combine albums with various artists (the detection is the hard part) or to provide an option to combine based on same album name (though issues would arise from same album names from different artists...)?
So in this case, these files are stored under the artist folder of the artist that is displayed in MuvUnder Cover?
In the meantime, you could click on the first displayed album of a various artist album (better if they are sorted by album title -> set in options), change the album name to "Various Artists" and then after it has found the artwork, click on that album, right-click -> copy, then select each of the other albums and paste the album artwork to each one of the other displayed artists for that album. If that didn't make sense and you need more clarification, let me know.