1933 R306 Butter Cream Babe Ruth
Like several issues of the 1930s, the sponsoring company was offering some VERY desirable free prizes if a child completed the entire set, and sent the cards back to the company for one of those prizes. This was the depths of The Great Depression, and the Butter Cream company was offering as a grand prize an outrageously desirable bicycle! Since the firm did not want to give out very many bicycles (maybe only 1??????), they super super super super super (you get it, I'm sure) short printed one card----"Babe" Ruth.
Perhaps as a last ditch effort to persuade a kid not to redeem the cards for the precious bicycle, they made the toughest to find card to complete a set the most desirable player of any kid who ever wanted a baseball card, the mighty Babe!
When you really think about it, that's pretty underhanded.
When I consulted my Beckett 3 Baseball Card Price Guide, the Babe Ruth was missing from the checklist. I guess it had yet to be discovered, or known by only a few people, in 1981!
In hobby lore, Barry Halper won this immensely rare card in an auction, and proceeded to lose track of it!!! As I understood the story, Barry accidently threw it out, with a bunch of other wrapping. I'll bet it took him a long time to get over that mistake.
If I got the story wrong, and someone wishes to tell it as it was, by all means, please do so.

--- Brian Powell