PQM's on paid first class...but standby on earlier flight
 

I've got a paid first class ticket coming up; I know I will earn 50% additional PQM's on the flights. But what if I go standby on an earlier flight on the return and there is no first class available? I'm not reticketing and I've still paid the first class fare...how will US view this flight when awarding additional PQM's / not awarding the additional PQM's?

The system will award you miles based on class of service flown. A call / email to customer service will rectify the situation and get the bonus miles awarded.

Are you sure about that? Wouldn't it be class of service paid? If it was class flown then why don't you get additional miles when buying an economy ticket but flying in first on a complimentary upgrade?

For the second question, they can tell by the fare bucket (e.g., O class for a complimentary elite domestic F upgrade from a coach fare) that it wasn't a paid F fare and won't award a class of service bonus.

The risk seems to be that the fare class might change if, for instance, you sit in coach on a paid F fare on a different flight where first wasn't available, which is what I believe gottigotti is referring to. In that case, the computer is likely to award miles on whatever fare class was used to seat you in the coach seat. Unfortunately I don't have a definitive answer to that. The correct answer might actually be to refund the difference between the coach and first fares rather than award additional elite-qualifying miles.

In my original question, I said I had paid for first but flown in coach.

I went through my flights and found two different scenarios:

1. I went standby on an earlier flight and was seated in coach when I'd paid first for the original flight.

2. I paid for first, and my flight was cancelled. I was moved off US and put on AA, and was on a flight with a connection instead of a direct flight.

So the first, I made a choice. On the second, I didn't...got more miles flown, but not the class of service bonus for the fare I paid and also received no refund for flying coach vs. first.