Before the release of Zero Year, I had heard a rumor that Batman only wasn't held to the 5 year timeline like everyone else and that he was allowed to have existed before Superman but only as someone working in the shadows. As long as Batman remained an urban legend/myth and not a public hero until Superman's debut, then it still worked.
I'm really sad that's no longer the case, because it allowed everything to work kinda. Now? Now we still don't even know if Tim Drake was ever Robin or if he went straight to Red Robin.