A notification engine manages subscriptions of applications to data events in a file-sharing environment. A subscription includes a data event recovery time stamp indicating the time when a first change to subscribed data objects occurred of which an application was not aware. When the data event occurs on a computer, the engine finds applications subscribed to that data event and sets the time stamp in the subscriptions for non-local applications to the current time if the data event recovery time stamp is clear. An application that was not notified of the data event that occurred on another computer learns about the data event when it is called back. The application uses a data event recovery time stamp indicated in the callback to issue a query for a current version of subscribed data objects to which data events occurred at or after the time indicated in the time stamp.