There’s the example I don’t know what to do with:
It is not immediately obvious that the cover art / release is unofficial. I checked some “samples” of mp3’s floating around - some of those have the cover embedded too.
Should something like this be
b) added as an "unofficial release"
c) added as a “normal release”, citing the most “official looking source” (in this case that would probably be “last.fm”?)
and if b/c:
How should the source of the cover art be documented? In this case, everything except for the cover art seems to be identical to the digital release available at the artist’s site… so…“Disambiguation”?
And more general / not only concerning this example:
Does it depend on how widely spread something is whether we want to add it here as OR ignore it? Where should the line be drawn? Or is this a case of: “If it’s out there, it should be added, even if there’s only 3 copies lying around somewhere”?