Charles,
There are other different characteristics with the Charleston Depot 2nd National CS flag but one notable feature is the white edging seems to be a lot wider around the cross than the other depot flags. You might be aware of this already but a distinct feature of a Richmond Depot 2nd National CS flag (or 3rd National CS flag for that matter) is the white edging surrounds the entire blue cross including the ends, whereas on the Staunton Depot and Charleston Depot flags the edging just outlines the arms of the cross leaving the ends of the cross touching the flag header and fly. Check out the MOC online flag collection, they have a few examples. Cheers