I recently booked a roundtrip in A, which had an underlying code of H outbound and W on the return. (/HAA00AQN/HAA00AQN/WAA00AZN/WAA00AZN)
Encountered irrops on the outbound, was rebooked into economy. After challenging this, I was placed on the "priority upgrade list," which apparently means you are on the gate upgrade list, but at the top. F was booked full, but had two no shows, so I made it into F.
The irrops leg posted as ZH with no COS bonuses. The others as A, with bonuses.