I thought the general understanding was that classical Aikido koshinage comes from the branch of Yagyu Shingan ryu that Ueshiba studied?
Why are you stating this as a fact?
Not so sure that koshinage has its origin in Yagyu-ryu. I think there is a good case that it in fact comes from the Soden waza taught by Sokaku Takeda. But I must admit I've never seen the Yagyu techinque attributed to koshinage. Maybe in biased toward Daito-ryu...if you could a link to he Yagyu technique would be helpful. I would love to see it. Take care. :0)
All the Best,