The Bad News
Unfortunately, Football Mogul doesn't yet have the automatic expansion feature found in Baseball Mogul. The NFL's messy history of franchise movement, expansion and contraction makes it harder to implement this for football than for baseball — so I'm still working out the bugs.
This means if you start a new game in 1961, the season schedules will be correct until you get to 1966 (when the NFL added the Falcons and the AFL added the Dolphins). On the bright side, if you add the Falcons and Dolphins at the start of 1966 (using the League Editor) the game will load the correct the schedule.