Other mistake: In the scene around the camp fire, Rob Roy can be clearly seen with with plasters on his hand.
Factual error: In two, maybe three scenes, there are ring-necked pheasants. One is early in the movie as the Jameses ride past a butcher shop where ducks and pheasants are hanging up for sale. One is mid-way in the movie in the scene of the house- or barn-raising and big picnic. The movie supposedly took place in the mid-1870s. Pheasants were not imported to America from China until 1881.
Factual error: At a very early point in the film, the King says something along the lines of "....and these are your playmates". In the background is a horde of 17th century ladies boating on the Achille Duchenne water parterre at Blenheim Palace. The palace wasn't built until the late 18th century, and the parterre was not designed until 1925.
Factual error: In the movie, Wild Bill has a shootout with the bad guys in the stables. He is holding two colt revolvers, each having the capability of holding six rounds each. However as a safety precaution, only five rounds were loaded in the revolver with the hammer resting on an empty chamber as a safety. Therefore, he could only have ten rounds total from the two colt revolvers. He fired far more than ten rounds without reloading.