Best practices for updating/changing prices on a Blanket Purchase Agreement

Can anyone help us to determine what the best practice would be for updating pricing on our agreements tied to Blanket Purchase Agremenets. We have a need to update our pricing, however, there is a period of time when the departments will still have invoices coming in from using the old pricing, and invoice coming in with new pricing.

If the buyers upload the new pricing, Accounts Payable may not be able to pay the invoice. Buyers tried uploading the text template with both old and new pricing and having an epxiration date on the old pricing, however, the upload accepted the new pricing with the expiration date.