relation between confirmation & GR date

Hi Friends,

I have one z report for on time delivery of vendor. wherein lines of the report are segrated as per the confirmed delivery date in the confirmation of the PO.

For example 1 purchase order item has 2 different confirmation  say 1 for 20.09.2014 for qty 3 & another confirmation  is for delivery on 25.09.2014 for qty 2.

In this report there is 1 column for goods receipt date. This date is suggested from the latest GR date for the item of the PO. So even if 1st confirmation is goods receipted on 20.09.2014 it is showing as receipted on 25.09.2014 this is wrong.

How can I relate Confirmation  with goods receipt.

Thanks,

Kiran