The Duchess of Richmond tells Wellington to keep Hay safe as she doesn't want Sarah to wear black before she's worn white - in other words, to have to mourn Hay's death before they're even married. However, white did not become routinely worn at weddings in the West until after 1840, when Queen Victoria's unconventional choice of that colour for her wedding dress made it fashionable.
As the camera pulls back and then upwards towards the right, in the first establishing shot of the British army after the sun has risen on June 18 (the day of the battle, with Hougoumont in the background), the shadow of the camera crew can be briefly seen on the cannon that it pans over.
Fred Jackson, who is present at the Duke of Richmond's Ball, but does not have a speaking part, is listed as the Prince of Brunswick in the credits. There never was a "prince" of Brunswick, but there was a duke, and he was 43 at the time of Waterloo (he was to be KIA at the battle of Quatres-Bras, two days before Waterloo, on June 16 at the age of 43 leading the small Brunswick corps). Jackson portrays a much younger man wearing the uniform of Willem, Prince of Orange (the crown prince of the Netherlands). The Prince of Orange was present at the ball and was on Wellington's staff as commander of the I Corps, and also commander-in-chief of all Netherlands forces.
At the opening of the campaign (just after Napoleon's "God's got nothing to do with it" comment), French troops are seen marching down the road and across the fields. Troops did not march-in-step whilst on the move across country. It was too tiring and inefficient. Route step (aka route march) was used instead, in which the troops remained in a loose formation, but did not match their steps.
The opening text states that "the combined armies of Austria, Russia, Prussia, and England" had recently defeated Napoleon at Leipzig. However, England did not participate in that battle. At the time of the battle, Wellington had just started an invasion of southern France (Leipzig is hundreds of miles away, in the middle of modern Germany). Interestingly, Sweden did fight at Leipzig (although their army was considerably smaller than each of the Austrian, Russian, and Prussian armies), but is not mentioned.
The British cavalry charge shown was actually carried out by the Union Brigade, which comprised three regiments of dragoons, the Royal Dragoons, the Royal North British Dragoons (Scots Greys) and the Inniskilling Dragoons and the Houshold brigade of heavy dragoons.
Some of the cavalrymen in the British cavalry charge can be seen to be carrying curved sabres, as dragoons they are heavy cavalry and should be carrying the straight bladed sabre. Sabres with curved blades were carried by light cavalry.
Reference is made to "Reille's Division". In fact, Reille commanded a corps (II), comprising three divisions present at Waterloo, of which the 6th was commanded by Napoleon's younger brother, Prince Jerome.
At the height of the battle, an ADCrelays a request for reinforcements from general Lambert at Hougoumont. Lambert's command was never in that vicinity but actually quite close to Wellington's main position near the crossroads.
William Howe DeLancey (Ian Ogilvy) is hot in the back by a ricocheting cannonball and he is seen with his back ripped open. In real life, DeLancey was hit in the back by a ricocheting cannonball, but it didn't break the skin but did cause massive internal damage including 8 broken ribs. He died from his wounds 8 days later.
Lord James Hay is first seen at the Duchess of Richmond's ball. Whilst Hay was at the ball, he was killed the very next day at the battle of Quatre Bras so he was not at the battle of Waterloo at all as this film implies.
During the scene where Napoleon and his staff see the advancing Prussians in the distance, where they raise their telescopes to their eyes, one officer on the right of the scene doesn't have a telescope and just pretends to raise one to his eye.
When the British return fire to the initial French cannonade with their cannons, the cannon on the extreme right moves backwards after a substantial amount of time has elapsed after it has fired, probably being pulled back by someone off screen, though this "effect" is not used in the following artillery scenes.
At least twice in the movie when French infantry are shown marching to the beats of drums that are played by young drummer boys, the tattoo beat by the drummer boys sounds clear and consistent, but close up shots of the drummer boys reveal that they are, in fact, just beating the drums randomly, if at all. Some of the boys seem to be barely able to march holding the drums, let alone play them, with such precision as heard in the movie's soundtrack.
When the Prussians are first seen advancing through the wheat field, the wheat in front of them is trampled down (presumably from previous takes of the shot or the route they took to get onto the other side of the hill)
The French soldiers when marching are stretching their foot as it moves forward and are swinging their arms with a little up-turned movement of the hand. This is how Russian soldiers march, not French.