Originally Posted by
diburning
Most if not all at-booking and OLCI offers do not book you into a higher earning fare. Offers at the "Manage Itinerary" page before OLCI and after booking are usually the fare difference, but YMMV as for whether it actually books into a higher earning fare.
The few (very few!) times I have taken the premium cabin upsell at booking, I got the higher PQMs/RDMs associated with the premium fare class (usually P/Z.)