1. There are a lot of smiths who signed with this name.
2. This is a big name in the sword world, and therefore often copied (forged). Not all smiths who signed using this name were great smiths, but several of them were.
The quality of the steel and smithing are the best I have seen from owning over a dozen antique samurai swords. How do I find out which smith actually signed this one and the approximate age. I will start doing comparison analysis this evening. Is there a particular source or book you would recommend?