Originally Posted by
MSPeconomist
If you buy a FC seat you earn RDMs and MQDs on the higher fare as well as 150% (or 200% for a FULL fare) MQMs. EXST doesn't earn any FF benefits or credit on DL.
From the page linked earlier in the thread:
SkyMiles credit is not automatically tracked for the purchase of an extra seat and must be requested by the SkyMiles member after travel.
Which suggests that RDM (if not MQD/MQM/MQS; though maybe even MQD can be earned through this?) can be earned from EXST.