In 2% of matches, the winner will have ``come back" from a situation during the game where their chances of winning were less than 2%.
There's nothing magic about 2% -- any small percentage works -- but I chose 2% because this should happen around once in 50 matches.
Of course such a comeback is unlikely in any given game, but whether it's unlikely to have ever happened in a Superbowl comes down to the issue
were the chances of NE winning ever much less than 2%, for instance when they were down 28-3 ?
I don't have access to the real-time gambling odds (please let me know if you do) but this commentary by Jeff Ma puts the lowest chance at 1%. That article focusses on strategy mistakes by the Falcons' coach, and few would disagree with that article's assessment. However his 1% estimate comes from simulating a game "taking into account the four variables of possession, down, distance, and score" based on historical data for team performance. Such methodology is rather unreliable in this context, simply because it does not take into account the possibility of strategy mistakes! I am inclined to assess the lowest chance as rather higher than 1%, so this comeback having occurred in some Superbowl is not unlikley.