During that period 91.2% of all cotton exported from the U.S. left from Southern ports, using the same statistics you're using. An overwhelming majority in anyone's book. Considering you can look at the fact that almost 95% of all tariffs were paid in Northern ports and somehow conclude that the vast majority of that was paid by Southern consumers, then I don't feel at all uncomfortable looking at 91.2% of all cotton leaving Southern ports and terming that 'virtually all'.
Do you see any meaning in posting that data other than to 'look smart'. Of course the majority of cotton bales left Southern ports...it was grown in the South, dummy.
From where else would it leave...Bangor, Maine?