One of the most valuable handwritten folio D-B Mus.ms. Bach P 803, stored in the Staatsbibliothek in Berlin, contains twenty-six layers, which are bound together. It is often associated with the name of Johann Ludwig Krebs, which for a long time gave the impression that the handwritten texts were also done by Krebs. The manuscript was indeed for a long time in Krebs’ house, and J. L. along with his father J. T. Krebs and J. G. Walther, as well as other lesser-known musicians, was one of the copyists. Of the twenty-six attachments, only the second (p. 9–23; further: P 803-II) contained a verbal text and tables with an interpretation of ornaments. It has not been possible to determine who was the copyist of P 803-II to date, and the concept of “anonymous copyist” has become anchored. In 1933, L. Landshoff turned to the tables with the performance of ornaments in P 803-II in connection with the interpretation of keyboard music by J. S. Bach, and forwarded the concept that the author of the text of P 803-II was the famous student of Bach J. L. Krebs. For the first time this myth was partially refuted by D. Wilson in 1979, who discovered the absolute similarity of the ornament Der Pralltriller oder Abzug in P 803-II and in the Clavierschule of G. S. Löhlein. Later Fr. Neumann wrote in more detail on this topic in his work on ornamentation (1978). The author also claimed that the anonymous copyist used the fourth edition of the Löhlein’s Klavierschule (1782) as a model for P 803-II. Thus, the assumption made by H. Zietz that P 803-II was based on the treatise by D. G. Türk (1789) turned out to be erroneous too. Studying these materials, the authors of this article drew attention to the many inaccuracies and false judgments associated with both the handwritten source P 803-II and the peculiarity of the anonymous scribe’s work with Löhlein’s text, as well as with many statements by the above-mentioned authors. It was shown that the third edition of the Löhlein’s manual on clavichord playing (1779) should have served as the primary basis for the anonymous copyist. Special attention was paid to inaccuracies and incorrect recommendations in connection with the interpretation of ornaments. A detailed consideration of the available realizations of ornaments in P 803-II and their interpretation will be established in the following second part of this paper.