I am convinced, rules like this border in complexity with the flight controls of the aircraft.
No, seriously. The quantity of seats are members of a grid of possible passengers. Here is one way of how it can work:
Lets take an AA
777 for example with the Atlantic configuration and you are wanting to go from coach to business class.
A quick look shows 35 business class seats on the AA
's interior of the 777. Of those seats, here is one possible way
of interpreting the "grid" I mention earlier.
Note: I don't know AA's specifics on this, but most airlines do it something like this
2 Seats: Discount coach fare to Business using AAdvantage miles
5 Seats: Full Fare Y coach to Business using AAdvantage miles
2 Seats: AAdvantage Reward Business (not upgraded)
15 Seats: For Sale only at full fare Business Fare (D/J)
8 Seats: For Sale only at disount business fare (I)
3 Seats: Reserved for transactions (usually rebookings or walk-up sales) wighing 2 days of departure
So, the 2 seats I listed up front may be the two you see and one of the ones you want!
Further, the upgrade or award tickets may be subject to "windowing" in time.
What I mean by that is lets say you want to book a reward trip way out to ensure schedule availability (I do this all the time) - 331 days out. That is as far out as you can book with the majors.
Lets also say you want premium product (First/Biz) as well. You may be the 1st transaction of ANY type for the flights you want - but the premium cabin may not be available. For example, I booked a reward ticket 331 days out from Grand Rapids to Orlando on Delta First Class the whole way up and back - but was waitlisted for one of my segments from GRR-CVG
. There was no other seat assignments in First or Coach! 3 months later, I cleared the waitlist - still just my wife and I confirmed in First Class on those flights.
Trust me, the planners at the airlines have very sophisticated modeling to maximize yeild, keep customers happy, and fill seats with passengers.
I hope this makes sense and clears it up for you.