Logic Pro 9 Undo history


Every time I open a project it seems that the undo history is empty. Is that because I had Preferences > Project Handling > Audio Backup set to 10 Project Versions?
Or does Logic wipe the undo history when quitting?
I just opened a project I haven't opened for a year or so and it is completely messed up. All the timing is off. It may be impossible to sort out, but if Logic had an undo history that went back far enough, such a thing might be overcome.