8mm Nambu oval or curved primer vs. flat primer

I have a few older Japanese production, post 1942, 8mm Nambu with glided metal, copper colored bullet with 3 primer crimps. Most all have a oval or curved primer (Center picture) but one cartridge has a flat primer. May be just pressed in the case harder? Possible reloaded however the bullet and bullet crimps look original.
Any ideas?

Thank you in advance.

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