To further clarify things, I'm not interested in potential duplicate books, only in potential duplicate authors.
My 'main' library is BEST and current working library is CALIBRE (yeah, I know...
). I want to copy to BEST books from CALIBRE with identical authors (single or multiple authors). With advanced option I just searched for identical authors, clicked OK and a I had a list of all the books I wanted.
Now, as I've said before it only tells me I have xxxx authors and the only option (that I know of) is to click on show details, save the log, manually search for the authors and go from there.