Hi
There is no direct relation between GR Stock w.r.t. PR request quantities,
because GR stock may made from multiple POs.
Maintain a ZTable which contains PR User, Material with Allowed Quantity.
During GR, increase quantity & GI, check details for authorized or not, if found, make GI posting & decrease quantity.
if quantity becomes 0, remove the record from ZTable.
Hope this will fulfill your requirement.
Regards,
Bisweswar