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I've seen a couple, or have somewhere, a couple of panels of Mathewson and McGraw that have a similar design. I want to say they were inserts in magazines or box bottoms from the late 1990's or early 2000. They may not be the exact same thing though.
That started out as one of the collectors' issue cards that were included in sheet form in issues of Baseball Card News back when it was owned by Allen Kaye. It looks like the Greenberg has been skinned and/or rebacked, as well as artificially aged.