In a rather humorous turn of events, less than 24 hours after finishing my first true backup, I accidentally dd’ed my boot drive while trying to solve other problems.
Mostly hilarious because none of the stuff really worth backing up was affected. Just system settings; stuff that’s a pain, but not a big deal.
With one exception. The database of my duplicati uploads was lost. I do have some of the early settings (all the login, encryption, not all of the folders and excludes).
So, what are my options? Can I just add all the folders I had uploaded to source and verify or recreate the database?
Also, side note: If I add /home/folder1/subfolder/ as a source, then later add /home/folder1/ as a source, how would the removal of /home/folder1/subfolder as a source be handled?
I suppose if you’re going to have a bad dd experience, that’s about as good a one as you can hope for. 
The good news is no - you don’t need to start over. Duplicati can repair/rebuild the local database by downloading files from the destination. Ideally it will only need the smaller dindex & dllist files, though if those are missing or damaged it may need to download some of the larger dblock files as well.
You should be able to (re)create your job (same destination, passphrase, etc.) then use the job Database menu to select Repair or Recreate. (If you try to do a backup before doing the repair you’ll likely get an error about unexpected files on the destination with a suggestion to do a Repair.)
Note that database Recreates (which this essentially is even though we’re calling it a Repair) CAN take a long time depending on source size / file count and hardware / bandwidth involved.
It will basically be ignored. Duplicati tracks files by absolute, not relative, path so as long as the path being removed is a subfolder of another source path Duplicati won’t care.
Just to be clear, this is JUST for source - changes like this in Filters are another matter entirely. 
Ok, great.
Ah, yeah. Obviously. Wasn’t sure what I was thinking.