Thanks to all for the great info.
Maybe the forging (drop forging) rough receiver was 'burned' in a few instances in that early faze of mfg'r.
Can't blame the final HT Dep't. for that problem.
But if I understand what's been posted already, the forging would have been brittle/hard from the 'burn'. Seems like the machine operations to follow would have rejected it for that condition.

This story surely will never go away.
Kind of like 'Is it safe to shoot my damascus barreled shotgun'.