You can use the reorganization function to get rid of outdated and/or obsolete planned independent requirements.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!
SAP Mental Notes 
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Is it recommended to clean up the old PIRs right away after changing the forecast consumption days, before we re run MRP, in order to see new PIRs re-created?
It doesn’t matter. Just make sure you do not remove PIRs within your consumption window.
Hi,
I liked the post on reorganization of planned independent requirements. I have one question though, do we always need to use MD74, MD75 and MD76 one after the other to complete the reorganization process?
In our system we have a background job that executes RM60RR20 (MD74) and RM60RR30 (MD75) in succession. However we do not run RM60RR40 which corresponds to MD75. Do we need to execute RM60RR40 ?
Thanks and Regards,
Sameer
where can I check what is my consumption window?, I might probably already know but since I am using SAP in spanish I have got lost in the translation
By the way, excelent material you have on your site
Hi , nice stuff once again, but what is that consumption window, please can you explain in detail