I am also noticing duplicates of artist names, for example, I have 2 10,000 maniacs studio albums, and 2 entries for artists named 10,000 maniacs. I have 3 "The Jam" artists listed in the artist listing !
This is a common problem with the AMG database. There were five of me when I first looked...
I had them correct it, now there are just two, and they can't get it lower than that at present because they are under two different genres. Their database is constantly under development and I've been told this whole problem will "go away" in the near future - perhaps because the artist-genre relationship will be more flexible?
I just have to add though that on my own sniffing around the web portals for all the databases, AMG has far and away the most complete database for classical repertoire (which is my area).