Luck more than anything. The JAL one was relatively easy. I booked a few speculative HND-DFW dates roughly 6 months ago when JL12 was still 777 service and before JAL stopped releasing more F award seats when they officially scheduled the A351. My May 1st HND-DFW booking was one of the (odd) A351 days that automatically carried over to the A351. The NH First one was a little more difficult but NH released a 2nd F award seat about 10 days before my April 29th target date. Interesting that they also released an F seat on the later 4/29 ORD-HND flight and it sat unclaimed for nearly a week.