The Sixth and Seventh Books of Moses is a compilation rather than a composition: seals, Hebrew and pseudo Hebrew divine names, angelic hierarchies and short operations, assembled from earlier grimoire material and printed cheaply in German in the nineteenth century. Judged as a text it is derivative and often garbled, and its Hebrew is frequently nonsense.
Judged by what it did, it is one of the most consequential magical books ever printed. It travelled with German emigration to Pennsylvania, where it fed the powwow or Braucherei tradition; and from American printing houses it reached African American hoodoo, where its seals became a standard part of the repertoire and where the mail order occult supply trade sold it in enormous numbers through the twentieth century. It reached the Caribbean and West Africa by the same commercial routes, and in parts of West Africa it acquired a formidable reputation and, in some places, legal attention.
The atlas records it as a living working text rather than as a historical curiosity. What is being used is the printed book itself, seals and all, and the traditions using it are living ones described here rather than instructed.
The title itself is the marketing. Six and seven were the numbers of the books of Moses missing from the Pentateuch, and a work claiming to supply them arrived with a pedigree it never had to argue for.