When a gun is reproofed, are the old proofs sometimes entirely removed?

I have seen guns that had additional proofs added after what I think were the originals - or at least I seem to remember that on at least one or three different guns. But I have an Evans that must be very early and it is nitro proofed and everything about the proofs scream very recent to me. There are no older proofs. Is this "normal"?

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BrentD, (Professor - just for Stan)

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