In this case there are three parties- Seller (of material), Buyer (of material) and Outsider(who discounts GRNs). There is one document i.e GRN.
Activity 1. Seller brings material to the Buyer
Activity2 Delivers material and takes a copy of Goods Received Note (GRN) issued by the buyer.
Activity 3 Seller again sells the GRN to an outsider for a discount.
Activity 4 The outsider buys several such GRNs from many sellers.
Activity 5 The outsider comes to the buyer on an appointed date (say monthly once).
Activity 6 The buyer pays the bearer (Outsider) the GRN
Therefore in my opinion the buyer has to make entries of GRNs in his accounts but should not operate the seller's account. In such case, can we consider GRN as a legally valid IOU?