States are initialized before the simpleInit is called.
If you try to access this state from another appstate by doing stateManager.getState(bla..) It's not yet there.
The best way to do it is to pass all needed appstates in the application constructor:
super(allMy, appSates, inThe, orderIWant, themTo, initialize);
then you'll be able to access any of them from the simpleInit of the application and you'll be able to access all previous states in the list from the initialize of one of them.
EDIT: Actually I'm wrong about the fact that they are initialized before the simpleInit, they are actually initialized the next frame they've been attached.
Anyway, the remark on the state order still stands.