There is only Ti, Da, Shuai & Na. The mechanics involved in each process do not vary from style to style, the emphasis on aspects of utilization & approach will. This is influenced by many things such as body type, mentality, social influences, cultural influences, tradition, mentality etc. As humans our approach to Ti, Da, Shuai & Na are subjective and as humans we like to over analyze and categorize each minute aspect of polarity shifts of basic principles to create something "new". Take "Elbow Up" for example, we have Bong Shou, Zhong Bong, Da Bong, Lan Shou, Gai Zhou, Pi Zhou etc. All variations on a theme, all elbow up positions based on different angles. Yes all require different "energy" but in the grand scheme of things it is still a gross concept of elbow up. It's our preferences that gives it value, but this value is only applicable on a personal level. Why are there so many versions of elbow up? Because one way does not work for all situations and for everyone, because of the various influences that affect our approach. As humans we will always chose the path of least resistance, but in varying degrees. Some use hardness, some softness, some both. Some use lots of technique some use very little. People will use what they are comfortable with and comes easy to them, there is also instinctual and habitual response. From birth we are conditioned in various ways. Each of us has a natural inclination towards one of the aspects of Ti, Da, Shuai & Na. No one approach (Snake body, 7 Stars, 7 Bows, 6 Harmonies etc.) is all inclusive, each method has specific mechanics of human motion. There is no omnipotent principle that will maximize the potential of all the mechanics involved in each method, each requires different attributes of human movement. Different body types, strengths, flexibility, ambulation & mentality will choose different approaches in principles to maximize their efforts. No one theory addresses them all, no one theory is better than another just different. Anyone who claims to have discovered an all inclusive method to maximize human potential is a liar, there are way too many variables to consider. That is why we have different approaches to Ti, Da, Shuai & Na in the martial arts. There is no one correct way.