I think you will have problems with the rules based on the start of your planned itinerary:
hkg-del-hkg-nrt-hkg
See this rule:
48N . 4. 1 INTERNATIONAL DEPARTURE AND 1 INTERNATIONAL
49N . ARRIVAL FROM/TO THE COUNTRY OF ORIGIN PERMITTED
50N . EXCEPT AS FOLLOWS:
51N .
52N .
53N . ORIGIN USA 2 PERMITTED. 1 ARRIVAL-DEPARTURE
54N . MUST BE A TRANSIT WITHOUT STOPOVER..
55N . NOTE: TRAVEL BETWEEN THE U.S.
56N . /CANADA IS NOT COUNTED AS
57N . INTERNATIONAL ARRIVAL/DEPARTURE.
Your itinerary has your departing HKG three times (to DEL, to NRT and then to LHR) and arriving three times (from DEL, from NRT and then from JFK).
These fares are frestricted by the rules to try to stop people having much flexibility in their country of origin except to get you to/from a convenient international gateway. And for HKG there is only one international gateway!
If you were to start in another country, you could then use HKG as a stopover and transit point.