Originally Posted by fastair

I understand, and since this part was answered correctly earlier, I felt no need to repeat it. What I wrote was to clarify where an earlier poster incorrectly brought "availability" into the discussion. The "Econonmy Full" is not tied to capacity or availability, but into the seat map and if there are seats available to be assigned. Yes, economy includes all of economy. There is only a "1st full" and "economy full", there is no breakdown into E+ or E-, as they are all a single cabin.

Availability is a planning thing, the seat map and the "economy full" is an operational thing that only gets generated once the flight is open for checkin.

Y=0 has nothing to do with it, no seats on the map has everything to do with it.