The traditional Chinese Feng Shui Pai - Teaching is passing down the "secrets" orally from master to disciple (Shifu Kou Zhuan Dizi 師父口傳弟子).
All Feng Shui practitioners honour Yang Yun Song 楊筠松 as the greatest Feng Shui Master of all time and claim that their Feng Shui technique comes from him. San He Pai claims that Yang was the founder of their school. San Yan Pai claims the same. They both say that the other school modified Yang's teaching to suit their purpose. They both claim they hold the real lineage from Yang.
A little mathematics will be enlightening.
Let us assume that Yang is the greatest Feng Shui master. How much of his knowledge did his disciples get? I would say that 90% is a generous number as none of his disciples is close to 90% as famous as he is. We also acknowledge that his disciples Liu Jiang Dong 劉江東, Ceng Wen Chan 曾文辿 were much more famous than their respective disciples as most of their names are unknown. Therefore, the assumption that each generation receives 90% of what the previous generation knows is a reasonably generous suggestion.
We further assume that from Yang Yun Song to today there are about 30-50 generations in between. How much does a present day lineage holder know even if we acknowledge that such a lineage exists?
0.9 ....= 0.042
We can safely conclude that the lineage holder today does not possess even 5% of Yang Yun Song's knowledge.