In the opening scene, someone can be seen eating a smoked turkey leg. Turkeys were indigenous to the Americas. The movie takes place during the 14th century, which means turkeys would not have been available in Europe until at least the 16th century.
In the very first joust the lord's daughter is seen looking bored with her hair styled in very large buns. A few shots later she is seen again, this time clapping her hands with the music and with significantly smaller hair. During the joust itself she is seen again with her in its original style.
While Adhemar is being prepared for the final joust, his page puts on his helmet and begins to close the visor with his ungloved hand. In the next shot, Adhemar closes the visor again with his own, gloved, right hand which, as far as we have seen, is already holding his lance (he is holding the horse's reins with his left hand).
In the final joust, after the first run with Adamar, William's armor is bent where the lance pierced his shoulder. At the next scene, the armor is in perfect condition, then later when he tells Kate to remove it because he can't breath, it is bent again.
When William first sees Jocelyn and follows her into the church (on horseback) there is scaffolding around the door and men working on it. Two minutes later when he is ejected by the clergy, the scaffolding has gone.
After the lord of the fist joust presents the golden feather on the pillow to William, he continues holding the pillow out as William shows it to the crowd. In the next shot of him, his hands are empty and he is clapping them.
In the final joust just before the first run, Adhemar shuts his helmet and you see a close up of his eyes through the slit. On the bottom right of the screen in this shot, you can see the top edge of his throat guard armor (and therefore its already attached to his helmet and shoulder). In the next shot however, his servant is seen affixing the throat guard to Adhemar.
In the final joust, Geoffrey sees that they need more time while Wat is strapping the lance to William's arm. He jumps up into the stand to make his introduction, which he does from the arm of the prince's chair. But in a reaction shot of John Thatcher, the arms are entirely Chaucer-free.
Right before William is told, instead of losing, to win the tournament for Jocelyn, William asks Wat if he remembers the church when they were kids. Wat's hair then changes from being down his forehead, to pushed back, between the shots.
In William's final joust with Adhemar, when his horse starts charging, Kate, Roland, and Wat run along behind his horse for a short period of time. As the shot changes you can see Wat standing still in the background. Then the shot changes back to the three running.
When William is in the stocks and Prince Edward makes himself known, Roland is shown with his head bowed and stick held down. A close up shot then shows Roland with the stick on his shoulder, as if he is ready to strike the Prince. Then, a wide shot is shown, as the Prince is approaching the stocks, Roland is shown in the original, docile position.
Although the movie is set in roughly the 14th century, one of the French characters is called "Quasimodo" as an insult when Will's friends are betting on him in the bar. Victor Hugo, whose story the name Quasimodo comes from, was not born until 1802.
When Count Adhemar comes to visit William in jail, he says, "He that strives to touch the stars, oft stumbles at a straw." He is quoting Edmund Spenser's poem The Shepheardes Calender, published in 1579. The story is only loosely set during the 14th century, but is off on this one by over 200 years.
This is a satirical romance, not a historical documentary. While nominally set in the middle of the 14th century (when Edward the Black Prince and Geoffrey Chaucer were active), it freely amalgamates the costume, custom and slang of many different centuries to create a unique world. The Chaucer character (who mentions his signature Canterbury Tales) bears almost no resemblance to his historical counterpart. Matte replicas of the London Eye and the Eiffel Tower are included to drive home the anachronistic intentions.
Chaucer has cloth stuffed up his left nostril to stop a nosebleed, which switches to the right side in one shot, and then back to the left again. Looking closely, it appears that the film has been reversed to keep the direction of movement constant as Chaucer backs away from Will - leaving it would have created a more jarring error.