You can use the reorganization function to get rid of outdated and/or obsolete planned independent requirements. Furthermore you can delete histories of the requirements from the database.
In these transactions you work with a key date. Requirements before this date are impacted by the transactions. It is possible that a Reorganization Period is set for your plant:
IMG > >Production>Production planning>Planned independent requirements > Define the reorganization interval
You enter here the number of days that the system subtracts from the system date to fix the key date. This setting overrides any manual key date that you enter in the transactions!