I believe you pretty much answered my question! I guess Pre-industrial Japan, no specific era or Shogunate. Lets say before the Tokugawa era for consideration sake (before the 17th. century).
Just curiosity Jon.... I just think this topic is interesting as hell!! knowing what I know now.. I guess we need to veer towards..
a) Has it always been a separate clan? Swormakers and Knifemakers (As it is now)?
b) "If" at some point they were the same... Did they use different source for steel? Distinction?
What do you think?