I haven't had this problem, unless artists can do something that looks identical to this on the face.
I had an artist take "Album 1", "Album 2", "Album 3", and "Album 4", which I purchased through a whole-discography purchase, and merge them into "Album 1-4". It turns out I was able to download the originals anyways.
I purchased a few albums from Ghost Mice, who deleted the albums or their account (and made a new one?). They are no longer downloadable. In the entry in my purchases history, it says:
> Deleted Artist
> Sorry, Strays by Ghost Mice is no longer available. Please contact Ghost Mice for more information.