Perhaps we might be hasty about assigning different origins to dhas based on the relative projection of the tips--at least without looking at a very large sample and considering their age too.
The older example posted by Khun Deng, for instance, has less of a projection at the edge than the spine, but it looks like a blade that has been used and resharpened over time. Since it is the edge and not the spine that is sharpened, the point would have a tendency to get shorter as material is removed (and perhaps rounder as in that example), but the spine would presumably remain more or less intact, saving the occasional ding.
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