i was able to book JFK-NRT in JL J just a few weeks ago, for a trip in march 2010.
when i booked this time last year for a flight in march 2009, JFK-NRT in JL J was impossible to get ... even booking 9 months in advance, there were no flights available for the whole of march! in the end i got an AA reward flight in J.
perhaps it is the economic downturn, with fewer pax in J.