1950 Bowmans
The Bowman cards of the 1950s contain two notable errors. The first was not technically an error, but nonetheless resulted in an anomaly in the 1954 Bowman set. The set featured Ted Williams as card number 66. Shortly after the set was released, Williams signed an exclusive contract with Topps, Bowman's primary competitor. Topps featured Williams as the first and last cards in their set that year. Now barred from using Williams's picture and name, Bowman substituted William's teammate Jimmy Piersall as card number 66 in all subsequent printings, duplicating the front and back of Piersall's other card in the series, number 210.
The next year, in their last set before selling out to Topps, Bowman "flipped" the backs of two pairs of cards. Brothers Milt Bolling of the Red Sox and Frank Bolling of the Tigers and pitchers Don Johnson of the Orioles and Ernie Johnson of the Braves were originally issued with their counterparts' card backs. Bowman corrected the error and issued cards with the correct backs.
Read more about this topic: Error Card