Regarding JAL, the new A350 F seems to starting to show some availability LHR-HND as a BA Avios redemption. I’ve seen single seats pop up three times on the route in the last week, typically about 11 to 12 days before departure. They don’t last very long: I missed out twice while my attention was diverted into,other things, but finally managed to snag a seat this morning at 9am for a 19th Dec departure that wasn’t showing when I last looked at about 1am this morning.

The older JAL 777 F come up more frequently, and remain available a little.longer, and often with multiple seats.