This is a topic that I'd like to find some facts, or at least some logical conclusions about.One occasion, I've come across tsuba, usually early tsuba (very early Edo or earlier) that have a narrow slot cut into the seppa-dai. This slot is not a WWII alteration for a "clip" on a gunto. It is intential and is about the width and thickness of tsuka ito. Its placement on the seppa-dai means it would be covered by a seppa if a seppa would be used. I've asked several sword world Japanese about this b