Mastering Wing Chun: The Keys to Ip Man's Kung Fu - Six And A Half Point Pole by Samuel Kwok

Leung Yee Tai exchanged Wing Chun techniques in exchange for learning the pole forms from Wong Wah Bo to gain stronger wrist and help make his Biu Gee stronger. This explains why the footwork is different in the rest of the Wing Chun System. When Leung Jan learned Wing Chun from Leung Yee Tai and Wong Wah Bo, it was quite unorganized and did not fit the Wing Chun System. Being a scholar and a doctor he added structure to the curriculum and created an order of progression.