Originally Posted by
othermaster
I once had a cash ticket in premium economy that I upgraded to Club with miles, then paid cash to upgrade at the airport to first. The agent at check-in assured me that I would get the tier points and Avios for first, but I only got them based on the original purchase of premium economy, so I am always very sceptical of airport upgrades.
This is an edge case as there was an Avios upgrade in it too. The agent was wrong and you were supposed to receive the original tier points and Avios associated with the underlying cash fare which in your case was premium economy.
If it was a cash ticket in CW upgraded to First at the airport you would receive First tier points and Avios.