User blog comment:BlueLantern1995/The Prophecies: What We Know and What is Logical/@comment-4509745-20121230225508/@comment-3146930-20121231010846

There have actually been a few promises. Percy promised that everything would turn out fine between the Greeks and Romans, which kind of blew up in his face. Chiron seems to have made an oath about something, but we don't know the specifics. Chiron also seemed ready to retire during The Lost Hero, so you have to wonder. Also, pretty much any oath made on the River Styx could count, as Annabeth made an oath to try her best to protect Percy back in The Sea of Monsters, meaning she could keep that oath until her final breath.

But as you said, we really don't know.