Why do removed Mobile Devices still show in the Inactive Devices and not Removed Devices Report? (4342236)

After removing a mobile device from the Exchange organization you will generally see the device show in the recently removed devices report. However, you notice that devices that were recently removed are still showing in the inactive devices report.

The nightly Online Maintenance that runs in Exchange has not yet run when MessageStats gathers information about that Exchange Server.
In Exchange 2003 & 2007 this runs by default from 1am - 5am.

The Online Maintenance runs nightly to perform a number of Exchange tasks. One of these tasks is removing objects from the Dumpster that have been deleted or are past their retention.

Resolution:
Schedule the MessageStats gathering for when after the Online Maintenance has run for this server or throughout your organization depending on the scope of the gathering you are running.