While I don't disagree with the above statement, how do you wise MTer's feel this applies to the lineage of a particular form that is taught across many styles? Do the subtle changes (which down the line become not subtle at all) from one style to the next restrict or just change the possibilities of the applications. I would like to exclude changes that were solely for athletic or aesthetic changes (i.e. changing kicks to the knee/groin/waist to kicks to the head).
Let's use Seisan as an example, since it is one of the oldest forms practiced across many Okinawan, Japanese, and Korean styles.
First I think you have to look to the source which is thought to have been White Crane Boxing from Fujian Province in Southern China where a number of Okinawan masters spent years learning the local fighting systems. Bushi Matsumura was one of the first to visit China and bring back knowledge that would be the basis for his system. Among his students, Anko Asato, Anko Itosu, Motobu Choki, Nabe Matsumura and Chotoku Kyan.
Aragaki was another and when you look at his most famous students it reads like 'Who's Who'. Among them men famous for developing the major Okinawan styles, Funakoshi Gichin, Higaonna Kanryo, Uechi Kanbun, and Mabuni Kenwa. So it is easy to understand how it is common across the karate spectrum.
Some of these guys, like Higaonna Kanryo and Uechi Kanbun, also went to China to further their study, so they would also have seen the form at its source.
In those days it seems the master would teach the kata in slightly different ways depending on the physical attributes of the student. Whether that came with different applications we will never know. But, if all these guys went away with a slightly different variation it is easy to see how the variation has occurred. But the most likely driver of change is when they stopped teaching the applications. Now anyone could vary the kata to suit themselves and no one is the wiser. Schoolboy karate as it was introduced into schools and universities and hence into the community could be anything.
In some ways it doesn't matter if it has changed and in others I would really like to know the original form. If your idea of kata is how you perform it in competition it doesn't matter at all. If you are trying to use it as a fighting system then it is more difficult, a bit like a back office Baffin sending out the wrong calibre ammunition to the battlefield. You waste time trying to work out why the gun doesn't work.
So, we have to work with what we have and try to use our knowledge of techniques to unravel the secrets of the kata we are studying, regardless of the variations. I haven't tried it, but, it might be possible to look across the spectrum at the differences to help with our understanding. :asian: