In Japan, it's not unusual for makers to keep a close eye on each other and adopt/copy each other's innovations. For example, I am told that Ashi-san (of Ashi Hamono) is famous in Sakai for the quality and consistency of his products so other makers try and emulate him.

For example, if you look closely at the handle and bolster design of the western-handled lines of Ashi, Yusuke, Konosuke, Kikuichi Performance and Ikkanshi Tadatsuna, as well as the SSG line sold by Sakai Ichimonji, you will see that they are nearly identical.