Originally Posted by
WillTravel4Food
When you purchase an upgrade on BA, the new fare class is used for calculating EQM/RDM. I've never learned the backend details of this, but it I can confirm by experience that it does work. There might be a misunderstanding by some people that because BA does this it's a common industry policy. It's not.
With BA it can depend on what type of upgrade IIRC. Many will code into fare classes that earn no miles.