O comando a seguir é provavelmente o que você está procurando:
duplicity collection-status file:///backup-folder
exemplo:
Found primary backup chain with matching signature chain: ------------------------- Chain start time: Mon Mar 4 10:37:27 2013 Chain end time: Fri Mar 15 15:42:22 2013 Number of contained backup sets: 3 Total number of contained volumes: 10 Type of backup set: Time: Num volumes: Full Mon Mar 4 10:37:27 2013 8 Incremental Fri Mar 8 15:53:07 2013 1 Incremental Fri Mar 15 15:42:22 2013 1 ------------------------- No orphaned or incomplete backup sets found.