Just remember if you jump up and down and say here is a black confederate, my response will likely be ok where are the other 199. In a million man CSA army, there is like to be some oddities; some failure on the behalf of a recruiting officer. In addition, there were members of State militias that were of African descent, but that is not the National CSA army. We know about those and the LA native guard.
No one is going to assert that the number of black confederates was zero, just that there is minimal evidence about a minimum number.