That's why flatness of a fired primer is a poor indication of pressure. I tested some Winchester white box M193 a few years back for a friend. He said he was getting 3340 fps from his 20" AR. That is a bit fast.
I stopped after 7 rounds as rounds 5 and 6 hit 68,300 psi. Average for the 7 rounds was 65,700 psi. Velocity was 3351 fps out of the 21" test barrel. That is a bit warm. Point is by the look of the primers, expasion ring and case head expansion measurements there was no indication of that much psi.
I have pressure tested thousand of rounds over the last 8 years and seldom consider condition of a fired primer anymore.