The technique is to define the range of statuses for which an object is readable/writable for each Role.
In the admin console, open each role in turn. Select the change item and open the details. On the 3rd tab (I think), you will see two fields where you can set a range of statuses. Make sure the end status of the range is the status before Completed.
If you are using folders, this needs to be done by folder, too.