Explanation about invoice reversal for standard price.

Question

Hi,
Please see the excerpt from SAP help below. I extracted this example in sap help found at http://help.sap.com/saphelp_47x200/helpdata/en/fc/85c5371e5db25fe10000009b38f8cf/frameset.htm
With regards to the example found below i dont understand why we cant do a simple reversal of the invoice 1 as follows :-
debit vendor account by 500
and credit GR/IR account by 500
Instead of the above simple reversal, the sap help is saying that we need to use a different stock value of 550. Can someone explain the following 2 questions :-
1) Why shd we use this 550 value instead of the 500?
2) What will go wrong if we use the value 500 to do the reversal?
Excerpt from SAP help :-
Goods receipt
=============
The stock account is posted with the receipt value based on the standard price.
Delivered qty X standard price
50 pcs X $10/pc = $500
The offsetting entry is posted to the GR/IR clearing account.
Invoice 1
=========
The GR/IR clearing account is cleared on the basis of the invoice price.
Invoiced qty X Invoice price
50 pcs X 10/pc = $500
The offsetting entry is posted to the vendor account.
Invoice 2
=========
The GR/IR clearing account is cleared on the basis of the invoice price.
Invoiced qty X Invoice price
50 pcs X 11/pc = $550
The offsetting entry is posted to the vendor account.
Reversal of invoice 1
=====================
The invoice quantity is greater than the goods receipt quantity. The credit memo quantity is covered by the quantity of the invoice surplus. The GR/IR clearing account is posted as follows:
qty X (Clearing value - goods receipt value / Invoice qty - Goods receipt qty) = 50 X (1050 - 500 / 100 - 50) = 550
The credit memo amount is posted to the vendor account. The credit memo amount is different to the posting on the GR/IR clearing account, so the difference is posted to the price difference account.

Answer 1

hi,
THis is because while making the credit memo, in your stock you don't have the stock coverage so till the stock coverage its posted to the GR/IR account while after that ie. the rest amount is posted to the PRD account...
If Credit memo is of 500 then, the system shd hit GR/IR account only..because there is a stoc kcoverage for the same...
If credit memo is for 550, then both GR/IR account and PRD will be hit...
Hope its clear...
Regards
Priyanka.P