Theoretically, the Flat Knob Short Tang (FKST) Superposed is much more rare than the Round Knob Long Tang (RKLT) Supers, but that doesn't make them more valuable. Rare, like "value" is in the eye of the seller and buyer as to what they think rare equals, even if it's described in a book as a source document. And the old saying, Caveat Emptor always applies.
But isn't that what makes hagglin' fun?

Scotty