As a bag handler for NWA maybe I can shed some light on the issue.

When you receive your bags in asia or europe the bags are generally loaded into containers and the flights have a dedicated container(s) for priority bags and are loaded at the door of the aircraft, thus are the first off and first dumped. It generally works the same way coming back to the states, the only exception being that sometimes some gate checks are loaded in the bulk compartment of the aircraft and take longer.

The problems come when there is a domestic flight, where there are a number of issues ranging from short turn times at the hubs to outsourced stations, and beleive it or not, actually not seeing the priority tag.

We honestly try to get the priority bags off first, but seperating them from the rest of the bags is sometimes harder than one can imagine especially in poor weather,plus we are trying to get everyone their bags as quickly as possible.