[Fiacha]

This is rather late but

At some point I told Calibre to keep its catalog in C:\Calibre books
At some later point I created a backup in D:\Calibre books and proceeded to ignore both directories.

After upgrading to 7.56 and then to 7.57 I eventually noticed that my count of books had dropped from 1300 to 300

I then checked the backup on D: and see that the missing books are sitting there.

I tried adding books from the backup on D: and they added successfully. However, the books are added to the backup catalog on D: rather than to the primary catalog on C:. The catalog on D: now contains old subdirectories with invalid index numbers and new directories with valid index numbers.

This leads to two questions
Why didn't they add to the primary catalog?
How would you suggest that I get to a clean catalog?
I am thinking of saving all of the books to disk, deleting the messed up catalog,
and adding the saved set. (The 'Use a bigger hammer' approach.)