[mitch13]

I run several "sub" libraries under my main Calibre library. In recent Calibre updates (unfortunately I cannot say which one) I have struck a problem. When copying a book to a sub library, I select the option to remove from the original library after it is copied. If that book existed already in the library being copied to, then Calibre would let me know that I was trying to send a duplicate book.
This does not happen, and I therefore end if with duplicates in the library I copied to.
Is there now something in 'Preferences' that would fix this?

Secondly, suggest/ask for a plugin that could run through a library and remove books that are not able to be read or loaded. Over the past few months, I have had terrible problems with two laptops. My Calibre libraries are held and run on a 4Tb portable hard drive. Between these laptops, I have managed/mangled my calibre libraries that I have been building for years. Consequently, I have a lot of books in the main and sub libraries that will not open to read. It takes too long to go through every book trying to read it to see if it is readable.
Help.
mitch13