I've been to all those sites at one time or the other. What citations they used are probably real and to some extent even accurate. But remember, even the vegetable tanned leathers we get today are different from the veg tans of 150 years ago.
And just to clear things up I do not doubt that cooking grease might have been used by soldiers in the field. That might have been all they had. Would you put cooking grease on your own shoes?
The black ball, I'm not real certain about. The recipe reminds me of "heel ball." Again, it's an "after market" product...maybe even a "folk remedy"...and it could have been just about anything. If someone told me their g-g-great grandfather swore by sorghum, who can gainsay that?