According to a post I saw, someone once asked at Ca. Grill and they said there were a few menu staples that "Disney won't allow them to change," but anything else can change at any time.
I know they don't do this anymore because I never saw it on their menu the last time I looked at it in person, but didn't they use to list a date when their current menu started and a date it would be ending on? I am sure I remember seeing that before.
I've got a few older CG menus lying around and there is a date at the bottom--most likely the date it was printed.
But since it's dated and printed on just a sheet of paper, makes it pretty easy to change a few things on short notice.