When the new catalogue of the works of Wolfgang Amadé Mozart is presented this Thursday by the publisher Breitkopf & Härtel and the International Mozarteum Foundation in Salzburg – a fundamentally revised version of the legendary Köchel catalogue – then at first only the experts will be amazed. But perhaps soon the musicians who play Mozart’s works and millions of listeners will also feel the effects. Because this is not just about questions of dating and notation, but also, for example, about which instruments the composer intended for a particular piece. Over the course of the 19th and 20th centuries, a number of things were changed that no longer corresponded to the original. But the problems began soon after Mozart’s death, when the sheet music fell into different hands and eventually into all parts of the world.