People have argued that they could have become legends afterwards etc, course the turtles are quite old by the end and there is a lot to start fixing.
As for it happening before, when Ciro said the bomb went off when the turtles were 21 it was the same time he was talking about his movie proposal (this is in the thread where people went to view the Monster Arc) He said the turtles come back out of hiding, I think they were going to be around 21 in this movie leading up to the bomb (they had gone back into hiding all this time, need to go back and check), so... if that is what the writers have in mind then they may not famous before the bomb either. (unless they were famous for the crossover arc and then hid from all the fans who wouldn't leave them alone LOL )
Personally I think it may be that when they came to write the end they have this story they really want to do they didn't want to let that one episode get in the way.
Oh, just one thing I did notice though, in the monster arc when asked about the outcome she told them she couldn't see the future as it was being changed by the events.... maybe that was the way out. Still, at the end of that she's tells Mikey he is yet to say the nicest thing anyone has ever said to her so maybe not.. I'm sticking with my above view
