On old computer, did you ever restore, or notice how many versions were on the home screen, e.g.
If you never finished a backup, that would do it. You could also notice by checking logs, emails, etc.
Deleting all dlist files by themselves is hard by design. You need to delete with allow-full-removal:
By default, the last fileset cannot be removed. This is a safeguard to make sure that all remote data is not deleted by a configuration mistake. Use this flag to disable that protection, such that all filesets can be deleted.
If you have historical records from Duplicati or S3, they might reveal things. Were dlist ever there?
If they were once there, the same records might show delete (manual or otherwise). If not, no guess.
In addition to the job database with random letters in name. Duplicati-server.sqlite is server database.
That’s where home screen stats are from, and they’re kind of sticky, maybe updated only by backups.
You might still be able to see something similar to image I posted, showing your old backup statistics.
The best you can do is look over the (default blocksize) 100 KB blocks, assuming dblock files decrypt.
Reassembly directions for what blocks should go into what source files are what the dlist contained.
Restore Backup with only dblock and dindex files is another opinion with a happy ending thanks to DB.
How many jobs do you have? Sometimes Duplicati backs up the database, e.g. at a DB upgrade time. Although it will probably be stale, and not matching current backup, it might contain some prior history.
If you’re a very good coder (like person above with happy ending), you might be able to get some files. Basically, see what else you have in the old database directory besides current job DB and server DB.
EDIT:
Did you ever do a command line backup? Those create databases that might be independent of GUI’s.