If you are using Cleanup submitted tasks tab and then do a SELECT in Database using clause WHERE created_time is earlier than date before which tasks should be cleaned up.
You might notice tasks that have created_time earlier than the picked date.
Why is that ?
Identity Manager any version.
The Cleanup submitted tasks task is run over last_action_time column value not created_time value
Which may seem like old tasks are not cleaned but they were touched recently.