A session value is a session value, so accessible from anywhere (on the server).
I think you will need to give more information on what you are doing, and what you are seeing, in order for me to give you more specific answers.
Bear in mind that if a user changes a field, and then clicks the next button, two events are triggered (one completing the field, one triggering the next button) and those two events might be being processed in "random" order.
Cheers
Bruce