Suppose you are viewing an assignment with an effective start date of 01-JAN-1987 and no effective end date. This means that the assignment was created or last changed on 1 January 1987, and the snapshot information you are viewing is still valid. There have been no changes to the assignment since 1 January 1987, and there are no future dated changes.
To find out whether the assignment existed before 1 January 1987, you should use DateTrack History.
If there is an effective end date, you know that the record was either deleted or changed on the next day. To find out whether the record continues to exist, you can set your effective date to the day after this end date, or use DateTrack History.
Note: It is possible to customize the information displayed in the Folder by modifying the DateTrack History view for the underlying table.
See: How To Create and Modify DateTrack History Views, (Oracle HRMS Implementation Guide)