[GMAN2222]

Does anyone know anything about these? I have been told that it is much more scarce than the original, as it is a "proof".
My research on the internet and on e-bay, has yielded no results, so I am inclined to think it is extremely scarce.
My research did bring me to this site, where I found some discussions regarding the 1953-1955 regular issue versions of the card, but unless I am mistaken, I didn't find anything regarding the "proof".
I am trying to get an idea of what it might bring at one of the nice auction houses. Hate to sell it, but.... sometimes you have to let go,,,
I know these are condition sensitive, this one just has a very minor stain (you have to look pretty hard to see it), and the card itself is very nice condition considering the age and delivery systems used to distribute the card.
Thanks in advance for any responses to this. I really appreciate the info.
I have many other rare cards as well, and as my curiosity gets aroused, I will find myself once again probing for more info :