Hi Amit,
Just to clarify Assen's answer; the "prior export" of IPR goods is allowed in case the customer requires the goods more urgently than the vendor can supply. In that case, if the trader already has stock in free-circulation, and provided there is no appreciable difference between that stock and the stock to be purchased from the IPR vendor (that's to say, the customer would find them equivalent, and could not prefer one above the other), the trader may supply the free-circulation stock and subsequently "back-fill" by importing to IPR.
The system models that equivalence by allowing the IPR stock quantity to go negative until such time as the new import to IPR is made.
Hope that helps.
Regards,
Dave