Originally Posted by
1K-SFO
I recently was ticketed on the AA codeshare SFO-LHR-SFO in World Traveler Plus (W). Both directions I purchased (at the check-in counter) a W->J upgrade and my ticket said J as the cabin/booking class. However, I was credited the normal mileage for a W ticket -- I did not receive any bonuses for being in J and my AA statement didn't show any record of J flown.
Thing being, such upgrades are similar to, say, SWUs. Your ticket may read Business or First, but your accrual will be based on the actual class you fully paid for. Conversely, you may choose to convert your fare, say from S (Deep Discount Econ) to J (Biz), by paying for the difference (in addition to the change fee) and only then you would earn under the new class.
Have not done this in codeshares, so won't venture into the guessing.