OK. I was reading the FL resize as distinct from the bump back, but it's actually the same body die.
It is normal with repeated neck sizing that the cases gradually get too tight to chamber and have to be sized down. How many rounds that takes depends on the pressure you are firing them at, so that could indeed be all that's happened there.
Once the cases are getting tight like that, how to they compare on the case headspace gauge? I would expect them to be pretty similar; all heading toward the same limit.
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