Hi David, I was watching that one too
The slots may very well mean something David, I'm just saying that the newer ones could be punched with a ready-made die. It would certainly speed things up. I've seen such dies in use and they do look identical.
The "persian" dagger looks like a Badik and the slots and holes are irregular. The khanjar l don't know, but the slots are very crisp and regular, and the alignment is restricted to a set of hole-slot-hole. The set closest to the tip does not look centred on the midline, while the two at the handle look like they are. This is why I think the maker or someone used a die-punch.
Just like you I would like to learn the significance of this arrangement, if there is any. The possibility I'm most comfortable with is brass (or whatever material) inserts in older blades. I don't think the slots mean anything on newer pieces and are merely there to sustain a "poison in the blade" story. Possibly in some cases the sets were added to old blades, who knows?
All the best,
Emanuel