a folder disappearing is different than a volume disappearing. Time machine tracks volumes by their UUID. (GUID?) So it knows quite well that you've plugged in a drive that has been gone awhile and is now back, and will NOT recopy the entire flash drive.

you can see this by unplugging a drive that's not excluded, and let TM run a few backups. If you browse to that folder on the TM drive, you'll see it there, in the most recent backups, as though it were still plugged in. As far as TM is concerned, it's still there, and nothing's changed on it until it determines otherwise. (when you next plug it back in)

To browse a disconnected drive in TM: open TM in finder, and opt-click or otherwise navigate all the way back to your computer, where you can see your hard drive listed, along with any other attached storage. (whether or not it's excluded)

Now click back ONCE. All attached volumes that are excluded should disappear AND you should see any volumes that weren't excluded, but are not currently present, pop into view. I see my club flash drive there. And it's back behind me sitting on a shelf, definitely not plugged in wink


I work for the Department of Redundancy Department