How many fights would have a different outcome had they been set for 15 rounds?

[LobowolfXXX]

Marvin Hagler was a great 15 round fighter,mind you he was
not a bad 12 round fighter, for those that could last with him.?
SLR v Hagler, those extra 3 round's would have been to much
for SRL.?

Leonard-Hagler was won at the negotiating table as much as it was won in the ring. Hagler needed the fight more than Leonard did, and he acceded to Leonard's team's demands for the conditions of the fight, including a bigger ring, bigger gloves, and 12 rounds instead of 15. All of those factors helped Leonard. I suspect that if those three things had been decided differently, Hagler would have won the fight.