RSword,
with all due respect, I think that the N°701 of plate XXI of Charles Buttin is really a Pesh Kabz. In his explanation he names it Pich-Qàbz.
I agree with you and Ariel, that knife must come from central Asia.
In the book "bei Shah emir und Khan" discribing the beautiful collection of Henri Moser, page 90, is a knife named "Ptshak". (I will try to join a photo) this is the closest I have found to the knife shown by Guy.
Nowhere have I found a blade with the same curve and cutting on the back and no back reinforcement as the the Pesh Quabz.
Regards
Michel