The award page even states
the following eligible fare types can be upgraded:
.
◾Premium Economy with published World Traveller Plus fares booked in W on British Airways
so for PE, only BA marketed flights can be upgraded
The only fares that meet that criterion are the most expensive offerings. An AA marketed booking would, by this rule, need to be rebooked to be BA marketed - the rebooking for a discount AA booking is not into W class
Last edited by Dave Noble; Aug 17, 2016 at 1:49 pm