Again, Dale, agreed. I didn't want to get to much into the history (kuden and written) of Koto and Gyokko, mainly because I considered it a little off-topic for a thread on Togakure Ryu, but for the record:
Both Gyokko and Koto Ryu trace their knowledge back to China in the 10th/11th Centuries, where, due to some major political upheaval, many members of the old Court and their supporters fled the country. In Gyokko Ryu's case, the skills went directly to Japan with Ikai (who may have been an individual, or a group of people with similar ideas), who then settled in the Iga region of Japan. Koto Ryu (or what would later be known as Koto Ryu), however, made it's way south to Korea, where it continued to grow until it ended up in the hands of Chan Busho (the school would also later take it's name from a story about Chan Busho, where he is said to have killed a tiger without any weapons).
Chan Busho, probably with a number of others (disciples?), made the journey to Japan, where again, the art grew until the knowledge came to Sakagami Taro Kunishige, the 10th Soke of Gyokko Ryu, who formalised the system (according to some theories, he was finding that Gyokko Ryu was no longer as effective for the changing battlefields in Japan, and Koto Ryu is his expression of what was needed. He is also credited with re-organising Gyokko Ryu at the time, changing it's name from Gyokko Ryu (Ninpo) to Gyokko Ryu Shitojutsu).
As a result, I would say Koto Ryu only truly existed from it's (the knowledge's) contact with the Gyokko Ryu knowledge. Certainly the skills which would form the basis of Koto Ryu have been around a lot longer (if we track things back even further, there are stories of the Koto Ryu skills in India [prior to it's time in China], where it was known as Karani, or Magical Technique, due to the realtive ease with which it's practitioners defeated other warriors), but to say that that was definatively Koto Ryu is a little misleading. Koto Ryu is Koto Ryu because of the path it has travelled, but it needed that last point of contact to become (mature into) the system we study.
With respect,
Chris Parker.