External disk reports incorrect amount of free space after doing clean up via terminal. DiskUtility's Repair temporarily fixes it, but why?
To back up a little for others, in the future.

How to get a report of remaining storage.

Via Terminal, type df -h and you’ll get a human-readable summary by volume in columns marked Used, Avail, and Capacity (as a percentage). (The Gi or Ti refers to gibibytes and tebibytes, base 2 units for a billion and trillion bytes instead of the base 10 gigabytes and terabytes.)



If these don’t agree, it’s likely a Spotlight error. Apple relies on Spotlight to mark and calculate remaining storage. You can delete the Spotlight index and rebuild it by following these steps:


Open the Spotlight preference pane.
Click the Privacy tab.
Drag the startup volume into the Privacy window.
Click OK at the warning, and the Spotlight index is deleted.
Select your startup volume in the privacy list, and click the - (minus) button.


That restarts indexing. This should reset your storage.