The scarcest and most valuable of the Kellogg's editions, the 75-card 1971 set was the only one not offered by the company on a mail-in basis. The only way to complete it was to buy ... and buy and buy ... boxes of cereal. Kellogg's again used the simulated 3-D effect in the cards' design, with the same result being many of the 2-1/4" x 3-1/2" cards are found today with cracks resulting from the cards' curling. A number of scarcer back variations exist. In addition, all 75 cards can be found with and without the 1970 date before the "Xograph" copyright line on the back; though there is no difference in value. - 2007 Standard Catalog of Baseball Cards, 16th Edition.