During "The Abduction from the Seraglio" performance, we see Kappelmeister Bonno watching from the box seat with two ladies flanking him. Milos Forman had the actors, including the extras in the adjacent box seat, remain in their positions to film a brief shot for a scene later in the movie (during "The Marriage of Figaro" opera, where we see Kappelmeister Bonno tapping his nose and smiling because the Emperor yawned). The result of this economical use of equipment and actors is that Kappelmeister Bonno, flanking ladies and extras all appear to have attended both operas sitting in the same seats and wearing the exact same clothing, wigs, jewelry and makeup.
Near the end when the bed-ridden Mozart is dictating a movement of his Requiem to Salieri, he tells him to write the bass instruments' notes as the "tonic and dominant" pitches in the key of A minor. But the notes that play, and the notes that actually appear in the score, are the tonic and sub-dominant.
At the first meeting of Mozart, Emperor Josef II finishes playing the march for Mozart and as he stands, he picks up the parchment from the piano. As Mozart kneels to kiss the Emperor's hand, the parchment is still held by the Emperor. When Mozart stands, the parchment is back on the piano, remaining there until the Emperor turns and steps back to pick it up.
When Mozart goes into the bedroom late at night to check on his son (and Stanzi awakens and looks at him), the candles on the candelabrum that he's holding are shorter before he goes into the bedroom than when he's in the room.
During the closing act of Don Giovanni, the jets of flame that appear underneath the backdrop change in height between shots, and sometimes disappear completely.
When asked to play in the style of Handel, Mozart says "I don't like him." He also states that Christoph Willibald Gluck "boring." In fact Wolfgang Amadeus Mozart admired George Frideric Handel, played and listened to his works frequently, and even re-orchestrated a number of Handel's works including "Messiah." Mozart was also fond of Gluck's work and wrote a celebrated set of variations on a theme from one of Gluck's operas (K. 455).
Mozart is shown being buried in a mass grave. This was not the practice at the time. A "common grave" was not a communal grave, but rather an individual grave for common people (not members of the aristocracy). By decree of Emperor Joseph II in 1784, common graves were unmarked and excavated for re-use after ten years. As a result, Constanze Mozart was unable to locate the grave only 17 years later.
Don Giovanni was not Mozart's "blackest" opera. Far from being dark, it was classified by Mozart himself as an opera buffa, or comic opera, and there's no evidence the Commendatore represents his father, Leopold.
A few mourners are shown at the city gates when Mozart is buried. The Viennese burial custom at the time was that nobody would attend a common burial (the burial of somebody who was not a member of the aristocracy) and would remain at the church after a funeral mass. The first written accounts of anybody attending the burial did not appear until 65 years later.
Don Giovanni premiered Prague, not Vienna.
At the beginning of the film, Salieri plays for the priest on what looks like a harpsichord, yet the sound produced is of a piano. This is not a goof. The instrument is in fact a pianoforte, which is also played by both the Emperor and Mozart at their first meeting. The pianoforte bridged the gap between the harpsichord of the 18th century and the grand piano of the late 19th century.
Josef II's title was Holy Roman Emperor, not Emperor of Austria as Salieri states. The name change to Emperor of Austria was proclaimed in 1806 by Josef's nephew Franz, but the Habsburgs were often called Austrian Emperor before this year.
This film is not a biopic. It is a work of historical fiction. Many of the events shown did not occur exactly as portrayed in the film, or happened at different times. Some did not take place at all and are included purely for dramatic purposes.
Severals scenes show the use of stage smoke, which looks like it was created with dry ice. While dry ice was not achieved until the 1800s, stage smoke through other means is recorded to have been used for instance on the Globe Theater as early as in the 16th century. We might assume that the production crew used dry ice to portray the smoke to not foul up the sets with noxious smells from "genuine" 18th century stage smoke.
Both Mozart and Salieri are shown conducting an orchestra in modern style, by standing in front and waving the arms. In the 18th century, the conductor played first violin or harpsichord, the other musicians watching his head and hand movements. It was the rise of large orchestras in the 19th century that forced the conductor to abandon his instrument and take a more visible position.
When Mozart performs in the orchestra for "The Magic Flute" he is shown playing the bell solo on a celesta. This instrument was not invented until 1886. The part should have been performed on a glockenspiel.
At the beginning of the film, the aged Salieri plays the first 18 notes of "Serenade No. 13 for strings in G" to the confessor, who then picks up the rest of the melody. "Serenade No. 13 for strings in G" (aka "Eine kleine Nachtmusik") was sold in 1799 by Mozart's widow to German composer Johann André, who published it in 1827, two years after Salieri died.
Schikaneder has Mozart play the party theme in the style of Johann Sebastian Bach, which the Viennese party crowd clearly recognizes. Although Wolfgang Amadeus Mozart was fond of Bach's work which he knew through his friendship with the composer's son, Bach's name and music would have been wholly unknown in the Vienna of the 1780s. Bach's music fell out of favor with performers, shortly after his death in 1750, and was revived only when Felix Mendelssohn promoted and popularized his work around 1830.
When Mozart is talking about the opera that will take place in a harem, he says it is set in "Turkey". In the 18th century, the Turkish country in question was called the "Ottoman Empire" and it did not take the name Turkey till 1920.
Near the end when the bed-ridden Mozart is dictating a movement of his Requiem to Salieri, he tells him to write the bass instruments' notes as the "tonic and dominant" pitches in the key of A minor. But the notes that play, and the notes that actually appear in the score, are the tonic and sub-dominant.
During the comic opera, a crew member is seen when the last of the small horses pops through the side wall. The person is wearing light colored pants and is standing behind the paper wall.
Wolfgang Amadeus Mozart was left handed, not right as portrayed by Tom Hulce, most noticeable when he's at the billiard table composing.
The Emperor Francis recalls an incident between the young Mozart and "My sister, Antoinette" - ie Marie Antoinette of French Revolution fame. That, however, was simply the French version of her name. Francis would still refer to his sister by her German birth name of (Maria) Antonia.
When Mozart is conducting "The Marriage of Figaro", the Emperor can be seen yawning in the background. He is shown yawning about two minutes later, and Salieri specifically states that the Emperor only yawned once during the performance.