Most erosion divots from pierced primers that I have seen have not been separated like that. They have run together more. Those look kind of "peened" but I can't think of any other cause. Very curious about what you find. A couple of years ago I had a bad batch of Winchester large rifle primers, which pierced in a Sako .243 and ruined the bolt in one afternoon of shooting. It took a while, but Winchester actually paid me for a $390 new bolt for the older Sako L579, after I sent the remaining primers back to them.... it was not easy to find that new bolt, either, which of course needed to be headspaced before use. That episode caused me to log my primers by lot number, which I had not done previously. Good luck!