Correspondence from behind the scenes gives an update:
"when Peter says that "Nigerians ground down the ends" he is mistaken. This was indicated by the van der Sleen beads, collected at Hebron in the late '50s or early '60s, that demonstrate the beads were MADE with flat ends."

The beads that van der Sleen collected in Hebron very likely had not travelled to Nigeria for grinding and then back again to Hebron. So I do feel this is pretty solid evidence that the beads were made in Hebron with flat ends. But I also feel that they did not flatten EVERY bead.