A very interesting weapon, also very interesting to TRY to use! About as hard to master as the cloth or leather sling! Take a bunch of practice!
I'd like to give a shot, sometime. I'm not into hunting, but it looks like it would be fun target practice.
I'm trying to imagine the right amount of rigidity on the dart. Making a nicely balanced one would be a reward in itself, it seems.
The flex is an important part of the whole system! A rigid dart is just another spear, less distance and power that way! If you have ever watched a super slo-mo of an arrow in flight, it also flexes like the dart, only not nearly as much! I never could hit a thing with either the atlatl or the shepherds sling! At least not very darned often! That was a while back when I was younger, in better shape and had better eye sight!
Maybe it helped to hunt something that was, literally, mammoth sized. ;)
I doubt it, since all his buddies were probably telling him that if you don't hit the hand sized KILL SPOT all you are going to do is piss him off! 
Could also have been 10 hunters and the other two got lucky and took one down while this one walked away with some very labor intensive points stuck in him! At least several hours of intense highly skilled work went into each of those points! Hey, that many guys can only carry so much meat, so forget the stubborn one!
crabbsaline
Atlatl