Poon Sing wasn't really Lee Koon Hung's sifu. This is somewhat of a misconception. When Sifu joined Poon Dik's school, he might have already passed away but we have been unable to completely verify this. At the time his school was being run mainly by two of his students. Leung Sai and Chow Bing. Poon Sing, I believe did teach there as well but was more busy handling other business matters. LKH got the bulk of his CLF from Leung Sai and Chow Bing. Not saying he didn't learn from Poon Sing as well but he never called him "sifu" only Sing Gor (Brother Sing). In fact they were Gip Bai Hing Dai (blood brothers). LKH also learned from So Kam Fook (his sisuk and younger classmate of Poon Dik) later on in life (in his 30s) and in the early days also learned some from Leung Siu Kuen (the nephew of Leung Kwai, one of Poon Dik's sifus).