0 != O
Usability fail: on the JAL web site, when you ask to see seat availability, they'll show an exact number on some instances and O when there's lots of seats (perhaps that's "O"pen?). But next to a number O looks like 0 and so every flight looks full.
And then, my surprise: I can't actually book a ticket on the JAL site directly. Buried on a help page I find: "(In the English site, online booking for International flights is unavailable.)". Ugh.