Very interesting observation on the ferrule. I am in accord with you both, the deeper ferrule seems to be characteristic of Eickhorn. I am of the opinion that this feature was grooved by hand and not cast into place. When you consider that, it's understandable that there are variations in depth. Further more the slotted tang nut is absolutely right. The only thing that can hold these pieces back a bit is ignorance of the variation.
Thanks Andrew for sharing your great assembly of daggers!