I think for some outports like ORD, there isn’t a rigid system of determining op-up priority. Rather, I believe the station manager (or whoever oversees the operations) have the discretion to choose some lucky passengers. I am claiming this because last June, all of my family (1GO 1OWS 2Not-even-AMs) was upgraded from PEY to J and we weren’t even on the same booking.

As a result I believe there must be someone in the back office selecting pax and sometimes it is based on more than just status.