@volumio-user I’ve not tried the naming scheme you suggested.
Similar issues, regarding display of album art, have been discussed on this thread.
The Rules Used To Find Local Artwork reassured me that I was looking in the right directories for album art and going about making it available in the right way.
I was just about to log a support request with Volumio when version 3.661 was released. While I’ve not yet done an exhaustive check, this version seems to have resolved my issues. It’s not clear from the changelog why this might be, but it is.