Just a question (on from this and up further) as to why the assumption the bulk of stopover time was spent in Japan? It seemed from the inquest questioning to SL (from memory), that it pointed to an extended stay in South Korea, rather than Japan (ie, did she have a special interest in the culture and/or food, that would explain a stopover there?). On the other hand, the questioning to RB was specifically directed toward a preponderance for overnight stopovers in Japan.
Drawing inferences and bearing in mind that we are dealing with imperfect info and they are not: it seems the prolonged amount of time for MB was spent South Korea and not Japan? Happy to invite discussion on this - it's not an area I've dwelt on, but a few furthers:
1997 - APEC cards were introduced, allowing frequent business travellers after pre-authorisation with member countries, to basically sail through DP channels. In, practice, (and from bitter experience) this meant on arrival an APEC card holder would wander through a separate channel with minimal scrutiny; non-card holders would join the general queue, meet up at baggage claim and proceed onward. And the member countries included: Australia, Japan and South Korea. You wouldn't need to see your co-traveller's PPT, if they were, in fact, travelling with you.
Also - travel Japan - last twenty years only, but they ticket your PPT on arrival, which has to be surrendered on departure. Just considering "stickies" for RB, and why the desire to avoid Japan post -'97.