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jeff sgiven the reuse of photographs and images in vintage cards (especially with caramel & tobacco issues, but this applies to 19th century as well), the line for rookie/minor-league can be drawn by the distinction made on the card.
you're right that some ambiguity is introduced here, but what if the Beckley cards were from two different sets? If for instance, all OJ cards had year indicators on them, and we considered '87 OJs to be of a different set than '88 OJs, as we do with Topps cards from year to year. Then the fact that the same image was used for both would not be relevant.