If a task has already successfully completed and you rerun it in the same day, it does not regather the information.
To reduce the impact on resource consumption, built-in gathering rules prevent a task from gathering information more than once within a single (UTC) day.
If you have made changes and want to have them immediately reflected in reports that day, you can use the Run Now with Override option to force a task to regather information.
In the MessageStats console right click on the task you want to run and select "Run now with Override"
For more information, see “Forcing an Update on Demand for Exchange” in the MessageStats Administrators Guide
