How many different versions are there?

Why are there different versions of kata? I have often wondered about this. When I first went to Okinawa--maybe twenty-five years ago now--I knew what I assumed was the Toguchi or Shoreikan version of the classical Goju-ryu canon of kata. Not entirely sure we did the Shoreikan version in all cases, since my teacher had trained in both the Shoreikan dojo and the Shodokan dojo of Higa Seiko sensei. But when I first went to Okinawa we trained in Shodokan dojos--with Gibo Seiki sensei and Higa Seikichi sensei. There were differences in kata. Not much in Saifa and only very small and somewhat insignificant differences in Seiunchin. (The back to back wrist technique that looks like an elbow attack was one difference.)

In Shisochin, there was a difference in how the forearm attacks were done that are most often (in most schools?) used as arm-bar techniques. There were also some stance differences, and the turning direction in the final technique was to the right instead of the left--a seemingly insignificant but actually quite important difference, seems to me.

In Seipai there seemed to be few differences of any consequence in the performance of the kata--though interestingly one was an extra turning over of the clasped hands at the beginning--but in Sanseiru there were many. In fact, this kata, with its controversial past, seemed to be the most varied. When I asked Gibo sensei about this, he laughed and said he knew seven different versions. In the Shoreikan version, for example, we had always stepped back at the beginning of the kata and were told it was to block a kick, grab the kick, and then both hands were raised up in front of the chest in a kind of "x" formation and rotated as one stepped forward to kick, etc.

How could different teachers who all had claims to having trained under the same person--Miyagi sensei in this case--practice different versions of the same kata? Some differences have profound influences on bunkai. Did some teachers favor certain bunkai and this, however subtly, affected the way they did kata? Did some teachers not learn bunkai, possibly affecting their understanding and performance of kata? Does bunkai inform kata or does kata inform bunkai? I don't know about historically what would be the case, but I have often seen people alter kata movement when performing applications against a partner and still call it bunkai. Would this, over time, affect how one did kata? Or did some teachers have physical idiosyncracies that their students mistakenly copied?

For example, after the opening three "punches" in Sanseiru, most schools perform a right open-hand block followed by a move where the left hand sweeps down along the right arm, stepping back into a long front stance. If you are told that this is a block of an opponent's kick, does this influence how you do kata? Could it also, over time, however subtly, influence various hand positions?

Why raise the question? Let me rather ask, is it logical for an attacker to initiate an attack with a low kick, especially from a distance that would allow one to block it this way? Is this even the best way to block a kick? If this is a lethal attack, why isn't one responding with a more lethal counterattack?