You maybe right...but in argument.
1. The good Dr. was an officer of the U.S.S.C, a group used to counting large bodies of men.
2. If I remember correctly the Union and Confederates counted combat soldiers differently. The Union counted all soldiers, the Confederates only those that were front line troops.
3. Your assuming that these were slaves and not freemen.
4. If I were in enemy territory I wouldn't be walking around without my weapon in my own hands.
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David Upton