This field in the Department Maintenance window date is the last time you ran the Department Report (RDE), Report Format A to shift sales and purchase history.
If your system uses a calendar year, the "date" in this field is the last month/year you ran the RDE with Report Format A. For example, if the actual calendar year is presently 2001, then January is 01/01 (the first period of calendar year 2001), February is 02/01 (the second period of calendar year 2001), etc.
However, If your system uses a fiscal year rather than a calendar year, the "date" in this field is really the last period/fiscal year you ran the RDE with Report Format A. For example, if your fiscal year starts in June, and the actual calendar year is presently 2001, then June is 01/02 (the first period of Fiscal year 2002), July is 02/02 (the second period of fiscal year 2002), etc.