With some of the differences in historical accounts of how the form was practiced at one time...
A rare video of Grandmaster Yang Ching Feng in his late 80`s demonstrating kuài Taijiquan 快太极拳 Grandmaster Yang was a graduate of the Xiamen Jing Wu school. He studied the three internal styles of Taijiquan, Baguazhang, Xingyiquan and was a student of Liu Jian Chuan who trained directly with the legendary Yang Cheng Fu.
Liu Jian Chuan earned his living as a bodyguard and claimed that the kuài Taijiquan form was a secret form from the Yang Family. The Yang family deny that this form is a legitimate part of the Yang style curriculum, even though in Douglas Wiles book titled "Yang Family Secret Transmissions"
it states "Not until late in Cheng Fu`s career did retention's of the Chen style jumps, flying kicks, stamps, change of pace, and shouts finally disappear from his form".
Wu T`u-nan, who in 1984 called himself the only living disciple of Yang Shao-hou makes reference to a secret family form for advanced applications with over 100 movements performed in only three minutes.