>T-24, FCM usually re-tickets to a new fare class and you receive MQD/MQM/RDM based on the new fare class

<T-24, FCM usually does not re-ticket and just ends up in an upgrade fare bucket which then credits based on underlying fare class

In either case if you do an upgrade and you see an upgrade fare class (OY, OZ, OX, whatever we're using these days with the new sub RUC classes) you are going to get credited based on the underlying, if you see a new revenue fare class you should get credited based on that revenue fare class.

As noted above MUA / GUC / RUC all book into the upgrade fare buckets which should credit based on underlying fare class, not class of service flown