And yet it all becomes crystal clear once you've flown the two products.

HKG-SFO is most definitely "BusinessFirst." They give you a blue duvet and a big pillow.

BOG-IAH is "United Business." They give you a blue kleenex and call it a blanket. No pillow.

Don't forget the soup course :p

DEN-ORD
 

What Route: DEN-ORD
Original Fare Bucket: H
Price Offered: $129
PCU/UFC: UFC
Where it was Offered: OLCI
Accepted: No

Declined the offer as there were 6 of 16 seats open at OLCI. I was #1 on the list and was still there at departure. F ended up booking full and I was in Y.

What Route: LHR-EWR
Original Fare Bucket: P/Z
Price Offered: $849 to upgrade to GF
Where it was Offered: In advance and at OLCI
Accepted: No

What Route: IAH-AMS
Original Fare Bucket: Z
Price Offered: $829
PCU/UFC: UFC
Where it was Offered: Airport Kiosk
Accepted: Yes

And this was also a case of dynamic pricing. Originally declined an OLCI offer that was slightly more ($857), then accepted when I got to the airport and had to check a bag. Change of mind had more to do with regretting the original decline and less to do with the $28 cost differential.

The plane was only a little over half full, and BF was less than half full, so I'm wondering if they got more desperate as we got closer to the departure time.

My return flight is also very empty. It will be interesting to see what they offer me on the way home.

That would have to be one outstanding bowl of soup. ;)

Your original fare bucket was Z? That's a business class fare.

My mistake. I think it was K, since that's what I have for my return segment. The upgraded fare code was ZN.

What Route: SAT-DEN
Original Fare Bucket: K
Price Offered: $259
PCU/UFC: UFC
Where it was Offered: OLCI
Accepted: No

If your upgraded fare class was ZN, your original fare was an N.

OK. Is N an economy fare? If so, that makes sense. My return trip is listed as K. Is it common to have different fare classes coming vs going?

Sorry, but I'm a bit of a novice here (obviously).

Yes different segments can have different fares. N is UA's cheapest published fare class. K is the third cheapest. So it sounds like you're on a well-discounted fare, making the $829 buy-up, ordinarily a bit high for Y-C, not such a bad deal.

NRT-ORD today.
Business to First.
$1159
Didn't bite.

$4856 SIN-YYZ via HKG and ORD
 

I've flown about 75K in the past year on UA, but credit to AC aeroplan, and this is the first time I've received an upsell offer:

March 14, 2014
$4856
SIN-HKG
HKG-ORD
ORD-YYZ
1 seat available on each flight

My fare buckets are K for the international legs, and L for ORD-YYZ

Could have gotten this for the round-trip in the first place, so it was an easy decline, as I've got a nice E+ seat.

I've got a quick question and sorry if this has been asked and answered. If I get an upsell to purchase an upgrade using miles and do so, would that flight still be eligible for earning miles and PQMs.

If so, would I earn miles at my originally booked class rate or my upgraded class rate?

I've got this offer:
LAS -> EWR
Original class booked: E
Miles to upgrade offer: 15,000 miles