That sounds like useful info, Jaimito, thanks.

I already found out that searching for one-way award flights at nwa.com doesn't work. I needed to use a round trip with a fictitious return date. I started looking at AMS-CPT next April/May and found economy available on one day only, with no business availability at all. I guess this mirrors FB availability and FB's curious inability to book more than 10 months ahead, in contrast to other airlines' 330 days.

I got much better results for a dummy LON-NYC, including DL LHR-JFK in BE.

There was a note saying that Worldperks members could get better availability. As a mere European, I'm not a Worldperks member.

I'll try again, armed with copious amounts of patience.