Forget the 1984 blockbuster film Amadeus. If you want to impress Mozart fans—who will doubtless be attending one of the Chicago Symphony Orchestra’s performances of his formidable Requiem on February 19, 20, 21, and 24—hit them with these three tidbits.

• In 1791, Count Franz von Walsegg commissioned Mozart to write a Requiem Mass, intending to pass it off as his own.
• Mozart died before completing the work, leaving only outlines for most of the piece. Scholars believe that the last bars he wrote were the first eight of the seventh movement, “Lacrimosa.”
• Franz Xaver Süssmayr, a student of Mozart, finished the most familiar version, but he never captured the young genius’s dramatic flair.