Aug. 11 is the birthday of Joseph Schuster (1748-1812), a largely forgotten figure but a member of an exclusive club: little-known composers whose music was mistaken for the work of a composer more well-known. In Schuster's case, it was the so-called "Milan" Quartets, string quartets that, for a long time, were thought to have been written by Mozart (who, in fact, admired Schuster's music).
Such misattributions have usually been based on stylistic rather than forensic criteria, assigning authorship based on family resemblance. Sometimes mistakes ran in actual families: The String Quintet formerly published as Joseph Haydn's Opus 88 was actually by Haydn's brother Michael (who also wrote a symphony once regarded as Mozart's 37th). Sometimes not: Friedrich Witt, whose so-called "Jena" Symphony was attributed to a young Beethoven, was no relation to Christian Friedrich Witt, whose Passacaglia in D minor was included in the first complete edition of the works of J. S. Bach.
Occasionally composers themselves perpetrated unwitting acts of misidentification. Brahms's "Variations on a Theme of Haydn" and Serge Rachmaninoff's "Variations on a Theme of Corelli" are based on tunes by neither Haydn (indeed, neither Haydn) nor Corelli.
Schuster, at least, was celebrated during his lifetime, especially for his skill in the light-opera-with-dialogue genre of singspiel, of which Mozart's "The Magic Flute" is now the best-known example. Some of Schuster's works were posthumously cataloged by his student Franz Schubert — no, not that Franz Schubert, but rather Franz Anton Schubert (1768-1824), the Dresden church musician. He, too, was a victim of mistaken composer identity: When publishers Breitkopf and Härtel rejected the more famous Schubert's now-famous song "Der Erlkönig," they accidentally returned the manuscript to Franz Anton Schubert, who was annoyed that "such trash," as he called it, was circulating under his name.