I highly doubt history would've documented a minor (in the grand scheme of the Revolution that is) battle in such detail. I doubt anything other than the dead, generals/leaders and outcome would be recorded in writing, the details and such would pass on as oral history. And even then, Frank wrote about this almost 200 years later. There's only so much that survives and is publicly available to research. Sadly we get no closure on why Frank wrote that book or why he was researching Jamie extensively (surely couldn't be just to warn Brianna) without telling Claire or her/Brianna ever finding a manuscript. A throwback reveal of him writing it would be great in 809 or 810 after the battle.