I have yet another problem. "a belief in black men willing to take up arms for the Confederate States goes back to the war itself". How do we know the newspaper publishers believed what they published. An editor just publishing a list of news items, does not necessarily believe those items. Accounts may be published for political reasons. Other than the articles, is there any evidence of belief?
don't forget stuff that's there just to fill the sheet. that are obviously short articles not much bigger than an ad - in fact they were often used for space reserved to ads when those ads weren't sold. they had a tendency to be hilarious and made up (women with two heads, talking horses called ed, black confederate brigates).
also in the 19th century papers printed a lot more fake news than we do today. the reason why we got better is simply because it has become a lot easier for paying customers to find us out if we serve bullshit (i guess it's okay to use that word when potus does it
).
that got nothing to do with spin, partizanship or outright probaganda, obviously. in the western world the english speaking papers and tv stations are the worst culprits in that respect. rachel maddow wouldn't make it a week and tucker carlson would probably be fired life on air in france or germany. boris johnson has been fired twice for lying by british papers but still he becomes pm - see the difference?
unless i did a piece about papers during the civil war i wouldn't dare to quote anything from those papers without either a hefty disclaimer or an independent corroboration. basicly the bigger the sold circulation the more trustworthy they are as there is a much higher chance someone finds out they print nonsense.
it's a bit like with wikipedia - those articles are a start and they definately are good to find ankles of research (names etc) but they aren't proving anything on their own.
having said that, to me a black confederate is anyone who
on their own free will volunteers any form of service to further the confederate cause - paid or not, free or not.
a slave who nurses back his wounded master is in my opinion not among those because he most likely does it from a personal connection with said master (might as well be fear for relatives if he let him die).
to get a number i accept a dunkelziffer (lit: dark number, like dark matter you can't prove it (yet)) of 90% for proven cases but i won't drop the requirement for their own free will.