Definition of effective date in purchase order

1) If the subsequent PO is a revised PO (i.e. revision of original PO), then date of revised order is the effective date of the PO. On the other hand, if a supplement PO is raised again, then both are independent documents.

2) For the supplier, if the original PO was accepted by him (but not the revised/subsequent PO), then effective date of PO would be the date of acceptance of original PO. But if the revised PO was accepted, then effective date would change to the date of acceptance of the revised PO.

It all depends upon your process. Revenue recognition standard works in its purview and first PO can be accepted, second po could also have been accepted. Or else, first po can be cancelled and reissued another new requisition can be acceptable. Dates, disclosure notes and editing them depends upon your software as well. This is because, if you close the period, all invoices cannot Ben modified. 

https://help.tallysolutions.com/article/Tally.ERP9/Tax_India/gst/gst_change_in_purchase_and_sale_price.htm

From the above you will find an example of how purchase amount can be increased against an invoice. 

Like this, software’s have different procedures and you can contact your manager for clarity is what I meant as well.