Thanks for the replies. I had not considered that this form of POUG would not earn tier points; I had assumed that they would be eligible in the same way as a regular BA POUG. I'm willing to accept the explanations that they are indeed not eligible Although it's a shame that BA couldn't just tell me this instead of stringing me along!

I still want to try and get the full 35 tier points as I understand that is the correct earning rate for economy even after 28 April? If you go on the flight calculator today and search for discount economy US Airways between PHL and PHX it returns 35 tier points with the disclaimer "The Avios and Tier Points shown are correct for flights booked from 28 April 2015."

It sounds like something mentioned in one of the linked threads whereby taking the online upgrade has actually put me in a fare class earning a reduced number of tier points. As far as I can tell I am still entitled to the full economy tier points as if I had not made any changes to the booking.