[1] From 1921 to 1931, the APFA/NFL determined its champion by overall win–loss record, with no playoff games;[2] ties were not counted in the winning percentage total.
[3] The APFA did not keep records of the 1920 season; they declared the Akron Pros, who finished the season with an 8–0–3 (8 wins, 0 losses, 3 ties) record, as the league's first champions by a vote of the owners.
[4] The 1932 NFL season resulted in a tie for first place between the Chicago Bears and Portsmouth Spartans, and could not be resolved by the typical win–loss system.
[2] In 1967, the NFL and the rival AFL agreed to merge, effective following the 1969 season;[5] as part of this deal, the NFL champion from 1966 to 1969 would play the AFL champion in an AFL–NFL World Championship Game in each of the four seasons before the completed merger.
The Packers were also the only team to win three straight championships, an achievement they accomplished twice: from 1929 to 1931 and from 1965 to 1967.