Wasn't the Daito-Ryu a family secret of Takedas that was thoguth to pretty much nobody?
Your right about that the art was a secret in the sence that they didn't have big school were they learned every ronin that came over. But instead during the big battles from 1500 to 1600, in which the art came to big use, before it was named Daito Ryu, it was used by the clan Takeda and later incorporated at the son's of the 2:nd Tokugawa shogun palace as the lifeguards MA there. This becaus it had showd it's effiectivness on the battlefield. Check out http://www.daito-ryu.org/index.html