The short answer is that it's hard. Which is why I buy all my vintage stars either graded or from my local, trusted shop. As for these two, the one on the left just looks too clean, too centered, the black is all perfect. I would immediately suspect reprint. The one on the right looks legit. It's more feel and experience than any one thing. The one on the right also appears to be a different card stock. It's easier when they're in hand. And I can't be sure....
Good luck. I love my 1965 Uecker.
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