These are the holders that the pro star postcard sets came in Blue for American league red for national league. As for the Seaver I am sure that I saw a poster sized version of this Seaver image but it seems it was not from pro stars.
As for the image on poster and postcard being different you here are the Stargell and Clemente postcards and you can easily see how different the signatures are on the two. They did a good job of placing the signatures on the posters on all white backgrounds so they stand out.
And I made sure to add Mercer for Yankee fans.
J
|