Patrick O'Brian created a fictional captain, put him on a fictional ship, and dropped him into the middle of real events that happened to other captains on other ships. He is widely regarded as one of the all-time masters of historical fiction, because the detail he put into his stories made the reader feel like they were on those ships during those events.
Almost all of the characters in Michael Shaara's The Killer Angels really lived, and really did the things they do in the book. Just about the only license Shaara took was to assign thoughts to his characters. He, too, did a masterful job of making the reader feel like they were at the Battle of Gettysburg.
I think our duty as historical novelists, whether we choose the O'Brian approach or the Shaara approach, is more to show the reader what it was like to live the events we describe than to be hyper-accurate in relating those events. Accuracy matters, to be sure--but I think people read historical fiction to live the history, and we may have to make stuff up from time to time to make that possible.
HN