I know this has been discussed before (at least in
this thread) but I wish it was possible to have multiple book of same format.
Something very bad happened in my case: Sometimes, for some books that I have 2 copies in let's say PDF format, I don't have time to check which version is better and I want to keep, so when adding to Calibre, I add one of them and after that I browse to the folder this book is stored in my Library and cut and paste the other pdf version as "Whatever_name_2.pdf". Now, I move some of my books to another Library inside Calibre and by doing this, Calibre has remove the second variant of my book!!!
And that happened to be the better one. Can you resolve this @Kovid