Hi, I think you can handle this through cycle count (physical inventory count) process and finally you can adjust those differences to process orders. This is applicable for both write off or write on the stocks.
I am not sure if you already have a process in place to handle the physical inventory count process.
SAP has already given a standard solution CKMDUVMAT to handle this scenario.
If not, you can manually post these differences to any new same product family orders (consumption reversal -262 through MB1A). That way you need not to go back and open the very old orders.
Hope this helps.
Regards,
Srinath
