This is what my AC source said, in response to your post (note- he/she has seen your post) - note, I am planning to purchase a Z fare ticket:

international fares have MPM ( maximum permitted mileages) and special fares allows specific routing like the YOW MIL permissible routing for the Z fare with a 30 days advance purchase.


In the top section of the example posted you will see MPM 4704, so it is the maximum permitted mileage without having to pay a surcharge ...