Hi,
Well what you can do is create a refresh button that will retrieve the new count of the library every time you click it.
All you have to do is add a Button then add a rule "Set a field's Value". "Field" being the textbox in which you want the number displayed ( in your case the one fitted with the count(ID) formula).
and "Value" should be set at "count(ID)" the ID field being the one from your Data connection.
Now add another action to the same rule to "Query for Data" using that same Data connection and you should be set.