Perhaps the kata was changed by Itosu before Chibanna learned it. As in most cases, the same kata is different from teacher to teacher, each putting their own spin on the kata. Maybe the Soken version is more in line with the way that Matsumura originally taught it. I can't say for sure. Soken was quite old when he returned to Okinawa and started teaching. Many times sensei will perform the kata differently when they get older,mainly because of the body changes, so they may eliminate or change movements so that if fits their body better. Some learn more of the hidden parts of the kata and teach the kata to show those hidden parts. In other instances they do not know or did not learn the hidden parts of the kata, so they change the kata to make more sense of the movements(angles of the strikes, vital point targets,etc.). I personally have not learned these versions of the kata, so I can not say for sure. Good question though.
