Most vendors operate with a "delivery date" being the date where the items are shipped from their site or most often based on Delivery terms. So depending on the Delivery terms (Incoterms)  the concept of delivery date changes. EXW often means a long lead time from shipment to delivery as opposed to DDP where shipment = delivery. There is a lot of misunderstanding with these concepts and that often leads to late deliveries... 

This means we need a similar feature on shipment and delivery as on the purchase order. Most vendors assume the delivery date is their shipment dates. It is a tough sell to change this, so a feature supporting this is sorely required and something we always do for our customers.