Question about Az shipping label, If I cancel and repurchase a label wil customer sees old tracking number or both?

When you cancel an existing shipping label and create a new one through Amazon Buy Shipping, the tracking number shown on the order will be the new tracking number only. The buyer will receive an email informing them that the tracking number has been updated. I don't see how this helps with Amazon notifying buyers that their order is delayed, however. You can only cancel the label on a shipment that hasn't yet been sent.