A planning system can receive media advertising orders including flexibility attributes indicating whether the orders are flexible with regard to various different circumstances. The planning system can obtain both booked an unbooked inventory from a traffic and billing system, and determine associations or re-associations between the advertising orders and the booked and unbooked inventory based on the flexibility attributes. The planning system can then generate a non-guaranteed order including the associations or re-associations, and transmit the order to media delivery system. The planning system can obtain feedback and/or real time data that can be used to reassess existing associations, and in some cases adjust the flexibility attribute values.