That is an excellent question but it is answered in the Organon by Dr. Hahnemann. The Organon went through six different revisions from 1810 to 1843. Dr. Hahnemann kept perfecting his original work. The reason there are differences in homeopathy because we practice by different versions of the Organon. Many homeopaths practice according to the principles of the 4th edition of the Organon. The last version of the Organon the 6th edition was actually not published until 1920 and Boericke's English translation appeared a year later in 1921. Each version of the Organon was based on Hahnemann's practice and constant research. Dr Hahnemann was constantly trying new methods and replacing earlier ones in his tireless search in an effort to provide the "rapid, gentle and permanent cure for his patients".
In 1828 the 4th edition was published and this was when Dr. Hahnemann introduced the single dose of one poppyseed. The 5th Edition was published in 1833 and this is where Hahnemann introduced and supported the use of High Potencies. Also in the 5th edition Hahnemann introduced frequent repetition of the remedy and administration of solutions in water instead of the single dry dose as in the 4th edition.
Now lastly in the 6th edition Hahnemann rejected everything he had written in the 5th edition. Hahnemann devoted the last 12 years of his life in perfecting his original method. The 6th Edition is where he introduces the LM potencies. In a footnote to Aphorism 246 of the 6th Edition Hahnemann explained that with each edition of his book he presented the best method that he knew at the time. However, after relentless research and experimentation in his own practice he revised earlier methods.
Hahnemann always gave one remedy at a time.