From 1961 through 1977, the NFL schedule consisted of fourteen regular season games played over fourteen weeks. Opening weekend typically was the weekend after Labor Day, or even two weekends after Labor Day. Teams played six, or even seven exhibition games. In 1978, the league changed the schedule to include sixteen regular season games and four exhibition games. From 1978-1989, the sixteen games were played over sixteen weeks.
In 1990, the NFL introduced a bye week to the schedule.
The "bye" in 1963 probably had something to do with assassination of Kennedy on November 22.