In the last three months I have started traveling quite a bit for work and am starting to pay attention to my mileage (up to 15 segments now and about 7K miles with another 3 trips planned in the next three weeks). Question is..I booked a flight two weeks ago and after arriving at the United Club had them (UC Rep) upgrade my seats to first class (I paid for the upgrade). I thought I should see some additional miles in my account for the upgrade but when checking it lists my fare class as ZN not F. Shouldnt these be F if I paid for the upgrade? Here is one of the segments I am wondering about:

Denver to Louisville -> Miles/Points (ZN/ZN)
Award Miles -> 1023
Bonus Miles -> 0