There are actually 2 'numbers' - the page name is automatically generated when the pages are created / duplicated. The page number is a numeric variable that stays consistent with how many pages you have.
You can change the page name to anything you want.
The page # stays what it is, and will update if you change the order of the pages.
To make use of this check out the new auto text features - there are tags for both page # and page name.
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