There are two variations of the Wham-O 10 mold in the All-American Model. They are differentiated by the copyright dates in the bottom tooling. Some have 1965 Copyright and are designated as 10-©65 and others have 1966 Copyright dates are are designated as 10-©66. The 10-©65 through various periods and re-tooling becomes the 20 Mold. The 10-©66 through various periods and re-tooling becomes the 21 Mold.
~Joe Essman