"Regiment muster rolls and rosters would seem to be able to answer some of these questions"

If they weren't sanitized by the compilers of the Combined muster rolls, which I have heard was the case because it contridicted popular conceptions of what the war was fought over. Not surprisingly most of the records which reflect the service of Black Confederates comes from lessor know sources such as the Trans Mississippi department where the records didn't get to Richmond. Or survived in state archives and pension claims records.