I don’t mean the historical events as such, which I know he would tweak for dramatic purposes - but the minutiae of a seaman’s life and work in age of sail, the language and manners of the officer’s class, and such.

I’m particularly curious because I’m a medical doctor, and I am continually amazed at the technical accuracy he displays with regard to medicine. He’s not just accurate, he’s accurate with respect to the times. Sometimes he has his ship’s doctor do the right thing medically, but for the wrong reasons that were prevalent in the day. Once he even got Dr. Stephen Maturin to choose what by modern standards would be the wrong treatment - and the patient died (in typical O’Brian fashion this was not explicitly spelled out - but a healthcare professional would have spotted it.)