Jampa Choephel
Edward,
I would suggest that the 47 pebbles would be the best amongst earlier and present Tibetan astrologers and next is 13 pebbles and these two systems are mainly accepted by the authentic tibetan astrologers. And "utpala snon po" and other are not that much famous within the Tibetan astrologers as my knowledge is concerned. Because the later were not documentary available.
There is also other ambiguity of “rgya bod skor ‘go sum chu” a second chapter of Moonlight text by dharma shri. In Chinese practice, there would have something similarity as we come to know from the commentary made by 5th Dalai Lama in His “rtis dkar nag gi dris lan nying ‘byed snang ba’i dbang po” My conclusion is that these were all the different systems of different practitioners. Because there have been so many religious advices and thus all these system come to existence.
Jampa Chophel