At times in the past, my impression is that "A" fares on some airlines have been similar to "YUP" and "BUP" fares on other airlines. At times these have been described as discounted F fares and at other times, as coach fares which allow you to sit in the F section. I seem to remember reading a thread in which someone on one of these fares was denied an F seat; I don't remember the resolution, but I think the bottom line was that an F seat is not guaranteed on these fares.