When enabling option to "Delete History Entries Older Than" X days (default 30 days). This function will remove computer history but it does not remove on-screen information and Job status for those jobs which are older than X days.
Stored procedure which is removing Old entries from database does not remove this Computer Event information.
Please find attached SQL query, which will modify existing Stored Procedure - so Computer Events older than 30 days will be also removed from the database.
NB!. Please backup your database before making any changes to default Stored Procedures.
Following Stored Procedure has been tested on 6.9 SP2 version.