Perhaps you copied the default local pst file to your USB drive, then used Data Management to point Outlook to the USB pst file, but left the original pst file in the default location. If you opened Outlook without the USB's pst file accessible, Outlook may have opened the original pst file from its default location.

If this is the case, you would only see the mail that was in the original (default) .pst file. You wouldn't see any of the more recent email that had been received while the USB pst file was being used by Outlook.

You might search for pst files on your local pc and the USB drive, review the file properties on any you find and note the size and Modified date/time of each. The larger and newer file may be the one with all the mail, and the one you should copy to Outlook's default location. Then have OL Data Management point to that file for your new coworker. (Before copying it, make sure you have a backup of the pst file in the default location first!!!)

I don't know enough about your situation to be more specific, but I hope that helps.

George