I wish the article contained some explanation of why the processing for NATS requires looking at both the ADEXP waypoints and the ICAO4444 waypoints (not a criticism per se, it may not have been addressed in the underlying report). Just looking at the ADEXP seems sufficient for the UK segment logic.
I'm guessing it has something to do with how ICAO4444 is technically human readable, and how in some meaningful sense, pilots and ATC staff "prefer" it. e.g., maybe all ICAO4444 waypoints are "significant" to humans (like international airports), whereas ADEXP waypoints are often "insignificant" (local airports, or even locations without any runway at all).
Of course with 20/20 hindsight, it seems obviously incorrect to loop through the ICAO4444 waypoints in their entirety, instead of "resuming" from an advanced position. But why look at them at all?
I'm guessing it has something to do with how ICAO4444 is technically human readable, and how in some meaningful sense, pilots and ATC staff "prefer" it. e.g., maybe all ICAO4444 waypoints are "significant" to humans (like international airports), whereas ADEXP waypoints are often "insignificant" (local airports, or even locations without any runway at all).
Of course with 20/20 hindsight, it seems obviously incorrect to loop through the ICAO4444 waypoints in their entirety, instead of "resuming" from an advanced position. But why look at them at all?