Originally Posted by
beerup
I don't think it's a matter that they *can't* show F1 J1 when there is one seat open in F and none in J. In fact, up until about a year or so, that's exactly how they did it. They also cross-list availability for farecodes within a cabin routinely (e.g., Y3 B2 would generally mean that only a total of three seats can be sold, not five). The new process is referred to as "cabin borrowing" and as you rightly describe it is the transfer of inventory from a higher cabin to a lower one when limited seats are available in the lower cabin. The reason I have heard it is done this way is to prevent triggering Sabre to designate the flight as overbooked. I imagine there may be other reasons that come into play too, such as more efficient inventory management (but just speculating).
While I am aware that they most certainly cross-list availability for farecodes within a cabin, I was not aware that they do it across cabins, and also did not see any change within the last year. There have been many times, for example, over the last several years, when (1) a 2-class domestic flight was showing F0 and Y>0, (2) the seatmap was showing unassigned seats in F and no (or very few) unassigned seats in Y, and (3) my sticker upgrade request cleared in advance of airport control, all suggesting that Y was in an oversold situation and F inventory had been restricted to allow more Y seats to be sold (since in a 2-class scenario, a Y seat is more likely to sell than an F seat).
In any event, I don't dispute what you say, and agree with you that clearly AA sometimes will restrict F inventory in order to be able to sell more J or Y seats.