Are you sure of this?
This is an assumption that has been made because it was a popular belief that Blacks did not serve in the Confederate army. Yet even the Official Records, Letters, Diarys and even photographs, say differently. You have Union records of Black Confedrates Prisoners being shot before they entered the gates of Camp Douglas in 1862.
This is my point. One set of records contridict another. People are saying that because their names do not appear in the CSR's they didn't really serve and that this is a Myth. So I guess that if the Official Records are at odds with the CSR's then we should throw out the Official Records? That that would be a bit silly too. No the most logically explaination for why the two records do not coexist is that there is an error in one and you said yourself that the CSR's are NOT comprehesive.
Again Fredrick, Maryland Sept. 1862, if 3,000 blacks who were walking, NOT driving wagons, are with Jackson's Corp, How many were with A.P.HILL's, and the other corp? What are they doing there? And we are talking about JUST the Army of Northern Virginia, while it was on a Campaign, when ALL unnecessary baggage would have been left behind in Virginia. Just to put it into perspective 3,000 men would have been the equal to maybe 2 Brigades, of 3 regiments of troops. That is a lot of "Camp Followers" to be tagging along with old Stonewall for no good military reason.
This thing that blacks didn't serve, or that they weren't recorded in the records is just another form of sanitization. I'll buy that maybe the records in Richmond were burned. I might even buy that the records of blacks in the Confederate military were handle in a different manner than being regularly mustered into service, but not all the records were in Richmond. You still should have records where balcks in service were far more common from the Army of Tennessee and even the Trans Mississippi who had better things to do that to try to run the blockade on the Mississippi river to get records to Richmond to be burned.