The Last Revision displays the last revision of any kind (to a record's attribute or the record's document), where as the Date Edited reflects when the record's document was edited (using the Edit Document feature through the viewer). These attributes can be added to the Visible Columns to view in the search results, or on the Revisions tab for individual record details. Just click Modify Columns, scroll to the Revisions section, select the attribute and click the plus sign.