I like discuss about various lineages of the Yang style Taijiquan.
Zhan Qin Lin was one of the best Yang Style masters (surely one of the top 10 ever)!
Zhan Qin Lin studied Taijiquan with Yang Jian Hou and Yang Cheng Fu, but latter he modified his Taijiquan acording of the teaching of the taoist Zou Yifeng. His disciples were Wang Yen Nien and Cheng Man Ching.
My opinion is that the style of Wang Yen Nien is not a secret Yang family style but a version of the Yang style that was created by Zhan Qin Lin with the modification of the authentic Yang movements with the supervision of the taoist Zou Yifeng.
That style is so different that can't be named Yang style! My opinion is that the Zhan Qin Lin's Taijiquan is very good, because he was known for his fighting abilities!
That is the true about the "Yang Family Hidden Tradition Taiji". If the changes were not made all by Zhan Qin Lin, the difference was made by Wang Yen Nien.
Cheng Man Ching also studied with Zhan Qin Lin, but his style is not so different from the authentic Yang as the Wang Yen Nien's. Maybe is true that Zhan Qin Lin did not teached him the "secred/modified" TJQ (how is said by Wang Yen Nien) or Wang Yen Nien made additional changes to the Zhan Qin Lin's TJQ.