Using Duplicity to extend Déjà Dup's functionality

Since Déjà Dup creates its backups using Duplicity, I thought I might be able to use Duplicity to do some things with a Déjà Dup archive that Déjà Dup can't do. Eg.:

Verify
Generate a list of archived files
Restore individual files or folders

So far my attempts have failed. The most frequent errors are "CollectionsError: No backup chains found" or "Remote file or directory does not exist in command='sftp...".

If what I am trying to do is impossible, please let me know so that I don't waste more time (and hope) trying to made this work. Otherwise, are there secrets I should know to do what I want?

Note: I am using a drive on a different computer on my home LAN as my backup destination. I have connected from Déjà Dup using either an FTP server or an SSH server.