This American serviceman visited their headquarters.
He said that their skill with the Khukuri knife was such because they use it for everything, including yard work.
He said that the bit about drawing blood every time they draw the Khukuri is a bit of a myth. Obviously they could not do this and use the knife for all kinds of daily activity.
He also asked about the notch at the base of the blade, he got many replies. My favorite, and his; "It represents the Yoni of the Goddess."
Be that as it may, these guys live with their Khukuri in hand. No wonder they're good with it.