Version 1.0.15 - 2015-12-04 New Menu Option: Attempt to Substitute Non-Responsive ISBN Using Author/Title [Selected Book]; Technical tweaks.
The new menu option may or may not find an ISBN. If it does, it often is an ISBN-10. If so, it must be converted to ISBN-13 (using the LC menu option to do so) before deriving DDC/LCC/etc. using the new ISBN.
If it does not find anything, you must either (a) configure Calibre's metadata download source to use ISNDB, which will require you to obtain an account key to enable up to 100 free Calibre lookups per day, or (b) manually search at
http://isbndb.com/ or elsewhere (e.g. Amazon or Google Books), and then manually update ISBN.
DaltonST