I found the safest way to do this is as follows:
- Move the indexed folder INTO the DT database
- Check the DT group contains all the documents and nothing is left in the Finder folder (the icon next to the group will change to show it is no longer indexed)
- Remove the Finder folder (everything is safely in DT)
- Export the group from DT to create a new folder in Finder with all the contents
- Check contents all in Finder (you will have both at this stage - all in DT and all in Finder)
- Delete the group in DT (it will move into DT trash)
- Leave it there for a day or two in case of any issues (so you still have a full copy in DTs trash)
- When happy, empty DT’s trash