If a simple update does not recreate the files in /usr/lib/cups/backend, do "sudo dpkg-reconfigure cupsys" and change one of the backend choices, then do "sudo dpkg-reconfigure cupsys" again and change this backend choice back. Do you have files in /usr/lib/cups/backend now?
If a simple update does not recreate the files in /usr/lib/ cups/backend, do "sudo dpkg-reconfigure cupsys" and change one of the backend choices, then do "sudo dpkg-reconfigure cupsys" again and change this backend choice back. Do you have files in /usr/lib/ cups/backend now?