Hi Jey,
According to the best practices you should close those old documents. If you have an old document and you don't want to consider this document in the MRP run, then I would think that the old document should not be opened.
Now if this can not be done and you still need to exclude orders, then you will need to create your own logic to exclude MRP elements during the execution of the MRP. For this you can use BADI MD_CHANGE_MRP_DATA.
Kind Regards,
Mariano