The revisions to APD ex-N Ireland apply only to direct flights. In the case of long-haul services, there is only a single direct flight ex-Belfast and that is United’s service to NYC Newark.
United threatened to quit Belfast some years ago unless APD was cut … which is what the N Ireland govt did.
So if you fly long-haul ex-Belfast via the UK, Holland etc then you pay standard UK rates of APD.
KLM is returning to Belfast after a gap of some years and last month the UK manager commented on the APD situation.