FWIW, whether Calibre names a writer's subfolder
Firstname_Lastname or
Lastname_Firstname depends on how the author's name is stated in the metadata for his/her individual books.
For example, if you have 5 Hemingway books in your Calibre Library, but some of those books state "Ernest Hemingway" as the author in the book's metadata, while other books state the author as "Hemingway, Ernest", then you will end up with
two folders for Hemingway books in Calibre:
One of the folders will be named
Ernest_Hemingway, and the other folder will be named
Hemingway,_Ernest.
However, the books themselves won't be duplicated inside the two subfolders -- each subfolder will contain different books by Hemingway, depending on how his name is stated in the metadata for a particular book.
That's why it makes sense to
unify how you state the writers' names inside metadata for books in your Calibre library. If you unify this, then you will only end up with
one subfolder for every writer, as it should be.
