In the Sept 2011 SMR (same one given out at National), there is an article on Joe Jackson. There is some discussion on a c.1908 Greenville Boy postcard that some claim to be his rookie card. I saw a similar thread on this here at:
Link
In that thread, it seemed like the card was also sold at a Mastro auction, so I tried to find the listing in the Legendary Auction archive, but could not. Instead I found a listing for a 1908 Philadelphia Athletics team postcard with Joe Jax here:
Link
Since Joe isn't in the Hall of Fame, he's not a part of the Old Cardboard reference. Is there a consensus on what is Jackson's rookie card or earliest known collectible? Thanks!