Hahnemann completed his work for the 6th edition in 1842, a year before his death. After Hahnemann’s death in 1843, his widow, Mélanie Hahnemann, had a hand-written copy made of Hahnemann’s volume and notes. In 1920, James Ward and William Boericke, American homeopaths based in San Francisco, purchased both the interleaved volume and the manuscript copy. Richard Haehl, a German homeopath, acted as their agent. Haehl used the hand-written copy as the basis for the 6th edition, published in Germany in 1921. The interleaved volume was sent to Boericke in San Francisco, and he used it as the basis of the 1922 English-language edition.
Digital facsimile of Haehl's manuscript from the Internet Archive at this link.