I'm a bit drunk, so I don;t know if I explain this right, but I'll try my best...
All my music in Z: ok?
So, in version 11, whenever I found an album apearing twice in my library, I would just locate on disk external for the double, erase it, then import again my Z: folder, and get rid of the double reference in my library also (I remember that window saying xx files removed)
No in version 12, importing [I think] is adding only.
How about removing?