Mark,
It looks to me like the boshi is an extension of the hamon, which is expected of Koto blades. I am going against the grain at the moment. Although literary searches by Jim, Klaus, and Peter only show Shinto smiths, the suguta suggests late Koto, and the boshi points to Koto. This is what radiologists would call a "discordant" finding. I am no expert, so please take my suggestion with a very large grain of salt.
Regards,
Hoanh