The Forrest quote about the blacks who served under him was made after the war as Williams' quote said and as such was, of course, not in the Official Records. But you knew that.
Of course I knew that. I'm not aware of any documentation of any kind by any Southern commander indicating the presence of black confederate soldiers until the last month or so of the rebellion. That's the point, there is no documentation that I'm aware of from the confederate side indicating the use of black soldiers. Which would indicate that claims of whole regiments of black confederate soldiers made earlier by other Southron supporters are most likely fantasy.