When Joan is in the torture chamber, they want her to sign the confession and she does not and lays the quill on the confession. Later, when staring at the spinning wheel with spikes, she drops the quill from her hand.
Joan is credited with saving France. While Joan was crucial in giving France the upper hand in the Hundred Years' War, it wasn't until Philippe, duc de Bourgogne (who, ironically, sold Joan to the English after his troops captured her at Compiègne), defected to Charles VII at the Congress at Arras in 1435 did the tide turn against England.
Joan's earlobes are pierced. Jewlery was a very important marker of social status in the 15th century, and most women of Joan's status could not afford such luxuries. There is no record of her wearing earrings.
The epilogue states Joan saved her country, France. Joan was from the Duchy of Bar, a principality of the Holy Roman Empire. The Duchy passed to the French crown in 1766 upon the death of Louis XV's father-in-law, Stanislaw Leszczynski.
Near the end, when two rocks are thrown through what is supposed to be a leaded glass window, it is clear from the way it breaks that it is just a regular pane of glass with lines drawn on it to simulate leaded glass.
In the 15th century, a priest can be seen wearing a Jesuit robe. The Jesuit order was founded in the 16th century.
Jeanne's hair is cut with pivoted scissors (the kind with finger holes), which were not commonly available until the 18th century. Spring-based scissors, which are squeezed from the ends, were used in the Middle Ages and were made of iron, not steel.
The soldiers wear helmets with modern chin straps (likely WWI British infantry helmets), not the Salle or Capelin helmets which would have been worn in the 15th century.
One of the priests is wearing a pair of black plastic spectacles.