Printed text booklets of vocal works by 17th and 18th century composers are often of immense importance for the study of their oeuvre, as the performance dates and places usually indicated on the title pages sometimes contain more precise information about the time of composition or the revival of a work than the autograph music manuscripts or contemporary copies. Surprisingly, the Russian National Library in St. Petersburg has recently proved to be a unique collection centre for these printed text sources. Many of them can be described as unical. They contain unknown versions of Johann Sebastian Bach's works. For some of these works, the date of composition had to be re-dated, with a deviation from the previous dating of up to 20 years. In addition, the newly discovered sources expand our fund of surviving texts for vocal works by Georg Philipp Telemann (including a hitherto unknown Passion Oratorio from 1731 as well as Kapitäns-Musik 1725, 1727 and 1733), Theodor Christlieb Reinhold, Carl Heinrich Graun, Christoph Graupner and other German composers. The convolutions also contain a number of compositions, including works by Georg Riedel as well as unknown motets by Johann Kuhnau. Several works by Michael Jacobi, Friedrich Funcke and Christian Flor have been rediscovered. The study aims to open up this treasure to the world and to contribute to expanding the knowledge of sources on German music of the 17th and 18th centuries.