Originally Posted by
MSPeconomist
My understanding is that inventory classes can continue to be "available" even if there are no applicable fares such as when it's too close to departure to satisfy advanced purchase requirements for all fares of that class.
Also a lot of airline inventory teams may close out lower classes on full flights regardless of the current fares in the market because of potential fares. There's usually a small to large communication gap between demand/inventory and pricing teams. If another carrier files a lower fare than currently in the market, the pricing analyst may match the fare. If I is open, you might all of a sudden have a selling fare where there wasn't before.