I think that - contrary to what I suggested as the protocol - we're now in fact trying to "explain" what he recorded and why he didn't record it earlier. As is usually the case, the simplest explanation is the best. I'm still trying to picture Howell Cobb riding in the midst of the equivalent to a large brigade of black men heavily armed. Something doesn't add up about Steiner's account.
But surely it's sensible to ask why he might record it either way - there's the "what he recorded is true and correct", and there's "what he recorded is outright fabrication", but in between there's "what he recorded is exaggerated/mistaken" and I think it's worth trying to see how there might be something underneath it which might be mistaken or exaggerated.
Which is a lot of how history is done with primary sources.
For example, I think we can agree that the account of Howell Cobb can't be entirely correct, because Cobb was not a major-general; at the same time, it can't be that this is a later addition by someone (i.e. Steiner) reading back Cobb's promotion, because the account was published in 1862 and Cobb didn't become a MG until 1863.
Based on the very small number of MGs with the Confederate army at the time (seven - Longstreet, McLaws, Anderson, Jackson, both Hills and Stuart) then if the account describes an actual event the balance of probability is that someone (Steiner or his source) didn't know that Confederate insignia was the same for generals regardless of grade. Having seen the insignia on (e.g.) known MG Jackson and then seeing it again on Cobb they'd assume it was MG rank for both.
For the presence of black armed Confederates, then based on the actual account it appears that not all of them were armed with muskets. The text of the account is:
Most of the negroes had arms , rifles , muskets , sabres , bowie - knives , dirks , etc. They were supplied , in many instances , with knapsacks , haversacks , canteens , etc. , and were manifestly an integral portion of the Southern Con federacy Army . They were seen riding on horses and mules , driving wagons , riding on caissons , in ambulances , with the staff of Generals , and promiscuously mixed up with all the rebel horde . The fact was patent , and rather interesting when considered in connection with the horror rebels express at the suggestion of black soldiers being employed for the National defence .
Based on this, then obviously if Steiner is making it up then he's making it up - but if what he's reporting bears some resemblance to the truth, then it might be that most of the men in question had
some kind of weapon (since he includes knives in the listing, which could be utility knives). Steiner is contrasting this with the Confederate aversion to black soldiers, and (again) he could well be making it up entirely, but if he's not making it up entirely then what he could quite reasonably be doing is conflating knives with rifles and including them both in the category of "armed" (while Howell Cobb would have seen nothing amiss with a slave or freedman servant working in logistics etc. having a knife - especially the freedmen servants, as that's what armed slave overseers mostly
were) in order to get in a dig against the Confederates and cast them as hypocrites.
Now, to bring this back to the strength report, it is obvious that Steiner's report may not be entirely accurate, but it is even more obvious that it's not entirely
inaccurate (in that the Confederate army manifestly did march through Frederick) and Steiner was there. Whatever the motive behind his calculation or the method by which he made it, 64,000 men for the Confederate main body did not seem preposterously high; indeed, if the whole Confederate army was no more than 45,000 men then the force that went through Frederick that day would have to be around 33,000, and would have taken half the time Steiner claimed to go past (and less than half the time claimed by the Baltimore Sun, which claimed 3AM to 9PM).
Does this mean we should take Steiner as gospel?*
No. It means however that we should take his report as the report of an
eyewitness, as he had the means and opportunity to observe the Confederate army, and is the only one who had a chance to see almost all of it file past the same place in one go - and not throw out his number entirely.
* of course, gospel
does involve conflicting and sometimes mutually incompatible accounts, so perhaps we should...