From my reading, the ticketed points are the places you fly between - not the ones you stopover in (as opposed to just layover or transfer).

With that in mind, how do they deal with this situation:

If an xONEx contains something like SIN-LHR-CDG, where the two flights connect on the same day/within 24 hours at LHR, I'm assuming that the ticketing carrier won't charge UK APD - perhaps this is wrong, but it would seem correct, right?

If I was then to move the LHR-CDG flight to two days later, so it's now a stopover in the UK, by the rules of xONEx it's not a change in ticketed points, so it wouldn't be a reissue and so would be a free change.

If I'm missing something, please do let me know.