Yes I agree that there maybe some errors in this article written in 2008. Since then, I have made more research and wrote a more detailed history in the magazine La Passsion des Couteaux Hors Série n°8 (october 2011). My primary sources are documents from the Miki Hardware Museum (especially an history of hardware and hirata knife from 1928) which I had translated and which seem to be the same sources as in your link, and Mr Motosuke Nagao himself who corroborated most and gave his family's version of the history.
Most history from the Internet, including from Japan, is rather sketchy I must say.