In the new version 4.0, about 400 of the 700 letters are recorded in full text. For example, the correspondence between Kurth and the musicologist and critic Alfred Einstein is collected in its entirety. Furthermore, letters from Max Auer, Joachim Beck, Paul Bekker, Joseph Dubowsky, August Halm, Leo Kestenberg, Armin Knab, Heinrich Langer, Alfred Lorenz, Henry Prunières and other important personalities are available in full text. The diverse collection of letters offers information on various questions about musical theory and allows insight into Ernst Kurth's private environment. An overview of Kurth's lectures in the years between 1912 and 1946 has also been documented.
Further additions include the correspondence between Kurth and Richard Flury, André Pirro and Hans Krill of the Max Hesse Verlag as well as Kurth's copy of "Grundlagen des linearen Kontrapunkts" with personal notes made on the new edition. In August of 2007, a collection of 76 images by August Halm was added to the inventory. These artworks were a gift from Hilda Halm to Ernst Kurth.