Dear,
Now coming to your requirement for creating & confirming Sales Order Quantity on past dates.This should ideally be possible, provided you have stock available in the system. Can you once again check whether stock was available in the system on the past date that you are selecting?
In OVZ9 ,check whether Receipts in past check box is left blank or any another is mentioned.
If you have any doubts please let me know.
Thanks,
Naren