Just to put the idea of 19-0 into context, here is some information from Pro-Football-Reference.com...
The NFL seasons go back to 1922.
- In that time, there have been 7 undefeated regular seasons.
- The 1922 Canton Bulldogs never lost, but tied twice.
- The 1923 Bulldogs never lost, but tied once.
- The 1929 Packers never lost, but tied once.
All three of those teams were champions, but there was no actual championship game.
- The 1934 Bears were undefeated and untied. They lost the championship game to the Giants.
- The 1942 Bears were undefeated and untied. They lost the championship game to Washington.
- The 2007 Patriots were undefeated and untied. They lost the championship game to the Giants.
The 1972 Dolphins are the only team in NFL history - 92 seasons - to go undefeated (and untied) and win an actual championship game.
The APFA was the kind of sketchy league that predated the NFL (2 seasons).
- The Akron Pros in 1920 were undefeated but tied three times.
The AAFC was the alternate league that operated in the mid-to-late 1940s (4 seasons, with a maximum of 8 teams).
- The 1948 Browns were undefeated, untied, and won it all.
The AFL never had a team go undefeated (10 seasons, started with 8 teams, maxed at 10).
The USFL never had a team go undefeated (3 seasons, between 12 and 18 teams).
So in 111 seasons of professional football...
- ...there have been a total of 6 teams that actually ended their seasons with no losses.
- ...there have been a total of 2 teams that ended their seasons with no losses or ties (and actually played a championship game).
- ...there has been 1 team that did it in the NFL as we know it today.
It's no coincidence that the vast majority of undefeated seasons occurred when the leagues were young and lacked parity, dominated by a small handful of major teams while other teams in the leagues struggled to stay afloat financially.