Happens to me relatively often in boxing and other less followed sports.
This is probably my favorite research piece. I spotted it in an auction of boxing photos, unremarked upon in the description:
The image was shot in December 1960 and the Clay team printed them up in this format for distribution to fans. The first run of about 100 was made in 1960, with additional printings thereafter. The signature is facsimile and was added some time after the initial print run. Obviously, no more were printed after he changed to Muhammad Ali.
I found this in a sportswriters archive from the late 1960s:
Turned out to be a Connie Hawkins pre-RC from his ABA days, part of a 1968 Minnesota Pipers team issue of 10 cards. Very tough to find.
This one I came to understand from boxing card collecting:
It is from a 1959 set issued in Argentina. I researched the set for my boxing book because it has some boxers. When I saw this one of HOFer Goose Tatum I understood just how rare it was. I nearly didn't get it. The seller misdirected it and it went from Argentina to NY back to Argentina then finally to me in L.A.
This one is a find:
I've been working on the 1925 Exhibit champions set for many years. The last few cards are obscure and tough. When this came to market I recognized it as from the set by its format so I went after it. Once I got the card I started to read up on the team and found out that it was coached by a HOFer, Ernest Blood. Further research confirmed that the dude on the far left with the 'stache is Blood, making this one of the earliest regular issue cards of a basketball HOFer.