First of all, what the heck is the difference between a rematch and a do-over?
Rematches are bouts in which the same two combatants lock horns for a second time. These are usually rivalries built upon one fighter's thirst for revenge or need to settle some score.
On the other hand, a do-over represents a hypothetical situation because it presupposes that the first fight didn't happen. So, a do-over is more about replaying a fight again to see if the outcome would be the same.
These are six fights that truthfully could have gone either way. They're toss-ups. If these bouts were played out several times in a row, the win-loss split would probably be pretty even between the two fighters.
Sure, some of these fighters may eventually get that rematch, but others will be left only to contemplate what could have been.