Other mistake: Isn't it weird how in the final scene with the 2 pirate ships, both of these ships are continuously blasting their cannons at each other, yet the sides of the ship show little to no damage throughout the entire battle? You would think that the parts of the ship that are in the direct line of fire would get hit.
Other mistake: Shortly after Morgan has successfully won William at the slave auction and they are trying to leave, armed soldiers begin closing in on them. As she attacks a couple in a doorway, we get a close-up of a nearby horse, who is wearing a 1902 Universal Pattern cavalry bit in his mouth. Not made until at least a couple of hundred years after the film is set.