Hi Brian,
Outstanding topic for discussion!! It seems almost ironic that specific elements of hilt construction are often ignored in discussions of the development of various hilt forms, yet they are often the most distinctive features in recognizing the forms themselves. I must admit I cannot place any examples of the crossguard you show prior to the 17th century but completely agree that they must date considerably earlier, and certainly among the sabres of Islamic regions as well as Eastern Europe. It seems that there were crossguards with langets on Turkish/Hungarian sabres of 16th c.*. It would seem the best course to follow would be the development of the langet itself.
It does not seem that the langet occurred on early forms of broadsword but later as hilts developed, a sort of rudimentary extension began to appear on lower part of the center of the guard. In some reading describing various hilts I have seen the 'slide' (langet) described specifically to secure the sword tightly in the scabbard, preventing excessive movement and dulling of the blade. This seems consistant with development of the sabres whose very effectiveness depended on their sharpness.
I agree that while the early dates of the swords seen in Yucel seem for the most part reliable, the mountings are certainly later and do not reflect the original mountings necessarily. It is difficult to rely on iconographic sources also, as the degree of license applied by the artist is indeterminable.
Although I cant offer much more here than is clearly already established, I'm glad you have brought this up, and as you have noted, the discussion can turn up compiled data from the resources among the guys here (beautifully evidenced already in the thread
!
As always, in wonderland....curioser, and curioser!!!!!
All the best,
Jim
* Wagner "Cut & Thrust Weapons" p.209, plate 4, line drawings only