Well, personally I have ever failed to understand how is it possible that the mahaira from ancient greece could be a direct model for the ottoman (or yes, call it balkan) yataghan wich compared in the 17th century? There is a whole middle age aka. 1500 years without any examples of such curvature between the two of them...
Well saying that the yataghan is the direct successor of the greek mahaira is verry much alike in saying that the newest two core intel processor is a direct descendant of the greek abakus...
Regardin' that assyrian separa, I would say that from the position and style of the handle and age of manufacture I would say that it has nothing to do with the knopesh, 'cos the knopesh was used like a sickle. Again there is too big time margin beteen the separa and the Laz bichagi to say that the one derives from the other.
My opinion is that the Laz Bichagi is an development over time from the classic yataghan and it is suitable only for the purpose of ship boarding. That would explain why is it so rare. And everyone who had managed one can tell you that it has a terrible balance and the curvature is so odd that you can easily miss your target. Further, the Laz Bichagi emerged anly at the nearly end of the 18th century...