The ones I have show that same "bald" area that you mention Stu, and also have the two threads coming off the bevo. It's not the test of all tests, but stick them under a blacklight and they will glow like they were made in Chernobyl if they are modern. Mine are all really dull under blacklight, almost grey. I have this one, and it definetly looks period, that shows the same characteristics on the reverse as the ones you posted. It shows three threads but it's a silver leader style.
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