You can see how the lineage chart is somewhat biased as they have Cheng Man-ching as being not a direct student of Yang Cheng-fu. Even Chen Wei-ming recognized Cheng's skill and he was considered Yang Cheng-fu's most loyal and long serving disciple. I do understand that Yang family politics managed to shuffle people around to make their own family look good, this is the case with Cheng Man-ching I feel as it was with Tian Shao-ling who actually studied under Yang Shao-huo and it was said under Yang Chien-huo, however they didn't want him looking better than Yang Cheng-fu I guess