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 difference is F and J are in two cabins, Y and B are not.