I don't know, I think the redskins comeback in 2017 may beat it. With the Dolphins it was a 21 deficit and the the comeback began in the 2nd qtr with 3 seconds left to make it 14. When it was 21 in the late 2nd the Saints win probability was only 6.1% and after we pulled to within 14 with :02 left in the 1st half, the win probability improved to 13% and only got better from then on. By the time their was only 6:00 left in the game, we were up 37-34 with a 80.3% win probability and again, it continued to improve as we expanded our lead.
With the Redskins game, when the Redskins scored with 5:58 left in the game to take a 14 pt lead, the Saints win prob. was 0.4% Even when we pulled to within 7 with 2:53 left, our win prob. was still only 3.8%, so even though it was 14 points instead of 21, the comeback didn't start until it was desperation time, I give the nod the the 17 Redskins comeback.