When Don Juan stabs de Lorca in their climactic fight, the knife is seen entering under his right rib cage in the area of the liver. In the next shot the knife is squarely in the middle of the sternum in the area of the heart.
When talking to the ambassador, Don Juan's earring is on the right ear, whereas for the rest of the movie it's on the left.
In the scene where Leporello is shaving Don Juan, he clearly completes shaving the right side of Juan's face. But when Juan takes the razor to complete the job, we once again see lather on the right side of his face.
When the ambassador seals the letter, he drips wax for the seal and there is a trailing drizzle of wax on the paper, but when Don Juan is handed the letter, the seal the firm and there is no trailing there.
When Errol and Alan are riding away from the Grouse hunting husband's castle shortly after the movie begins, they cross a small creek wearing the garb of Robin Hood and Little John. One can clearly see Robin's bow and quiver that Errol wore in The Adventures of Robin Hood (1938).
Sealing wax is NOT liquid at room temperature, otherwise it could never be used as a security sealing for correspondence (it would not take the stamp and would run off the paper it was supposed to seal). Sealing wax was usually in the form of a stick and would be placed over a flame (usually a candle). It would then be put over the seam of the correspondence creating a small "puddle" and then the stamp was pressed into it as it cooled to create the wax seal.
The film is set in the early 17th century when the predominant sword was the rapier. But all the characters in this film use fencing foils, which could never pass for a rapier. The rapier was a narrow, but broad blade, while the foil was long and narrow "blade" which flexes (so that when thrust against the fencer's opponent, it would bow rather than penetrate). The foil was created to teach students to fence when swords had evolved into the small sword. It was the small sword the foil was modeled to mimic, and so it is the small sword for which a foil could pass. BUT the small sword had yet to evolve in the 17th century and only became predominate by the middle of the 18th century.
There are several references to the city of St. Petersburg, Russia, in this film set during the reign of Queen Elizabeth I. The said city was not founded until a century AFTER that queen's death in 1603.
In the scene where the ambassador tells Don Juan that he is to return to Spain, the ambassador wears the stiff collar called golilla, an item of clothing that belongs to the reign of Philip IV, which started in 1621. The story of this movie takes place during the reign of Elizabeth I of England, who died in 1603.
King Philip and many of his courtiers, as well as courtiers of Elizabeth I, wear the wide brimmed feathered musketeer hat, a fashion of later in the 17th century. The correct fashion for the period, which several characters indeed wear, was a beret decorated with a feather, a look that would last a couple of decades into the beginning of the 17th century.
When Don Juan and Countess Elena are in the garden, the rubber soles of Don Juan's boots are clearly visible.
In most sword fighting scenes, it is obvious that harmless blunted competition epees are being used, not real swords with pointed tips.