Revealing mistake: The cannons shown are firing blank charges, which produce no recoil. Recoil has been simulated by towing the guns backwards when they fire. The problem is, there is always a distinct delay between the discharge and the "recoil." The cannon also seem to largely fire explosive shells. At no point do we actually see a cannon ball rolling or bouncing along the ground or into any group of soldiers.
Revealing mistake: During the battle, both the Allied and French commands spot unknown troops marching towards the battlefield. They are marching through what looks like a wheatfield, following paths which have already been made. However, these new troops are marching on a route so far unused by either the French or Allied armies, so therefore the field should have been untouched - these paths were made on the first take.
Answer: I think the film's dramatisation of this particular incident, when the French army defected from the restored Bourbon royal family back to the Emperor Napoleon might owe something to the painting NAPOLEON RETURNED painted in 1818 by Charles Steuben (also called Charles De Steuben and Karl Steuben) a German who became a nationalised (and patriotic) Frenchman https://commons.wikimedia.org/wiki/File:Napoleon_returned.jpg.
Rob Halliday