A set I've learned about semi recently is the 1950 Dominican Republic Album cards. They were a set released to paste in an album. There are a ton of Major leaguers in the set, but as I know only one or 2 finds have ever been known of them, and most of the cards are unique. So while the checklists have names like Rizzuto, Schoendienst, Berra, Jackie, Hodges etc. The checklist is equally as non complete, missing players like Williams, DiMaggio, Doby etc.
There are even retired players in the set known. Hack Wilson, Carl Hubbell. This can open another can of worms for pretty much any hof name.
