UGA a few years back managed 15-0. That is really unlikely, I think, possible, but unlikely. You'd think they probably blasted inferior opponents, but they needed a rather remarkable comeback to beat Missouri, a mediocre team, 26-22. They handled everyone else reasonably well, Kent State was about their second closest RS win at 39-22. Then of course they needed a flat miracle to beat Ohio State. So, presume they really were the "best team" that year, they could easily have been 12-1 and eliminated in round one.
You need breaks to go undefeated, some lesser teams have a shot at tripping you up.