Historical accuracy is rather important to me, as I gather it is to you, for the simple reason that it makes the story more believable. Personally though, I much prefer a woman to be completely naked in a whipping scene. I think until the time of Queen Elizabeth, that old spoil-sport, women were whipped completely naked at the cart's tail. She mandated that women only be bare from the waist upward. I've read that in the colonies (U.S.) of the 17th century, occasionally women were whipped naked: for instance Quakers were considered heretics in some colonies and were stripped bare and whipped. They might also be branded or executed. I suppose in any era, it would not be unusual for a slave to be whipped naked. So there's that. Personally, I always love it when an author acknowledges an historical actuality, or "rule," and then explains why, in this particular instance, it's going to be violated. I mean, just give me a reason to believe.