As a basis for some investigation/discussion, could I wonder aloud whether it is, perhaps, a futile effort to analyse the Suttas as if they were constructed as a logical exposition with exact, constant, definitions?
That could be argued to be extremely unlikely, since they were oral Dhamma talks, designed to liberate, not scholarly essays.
Regarding the current topic, a "common-sense" way of regarding the fact that sometimes the suttas speak of "upādānakkhandha" and sometimes just "khandha" would be that that's just how it came out in various circumstances. Similarly, sometimes (e.g. in the Satipatthana Sutta) listeners are urged to regard both internal and external khandas (or elements, etc), so perhaps the interpretation that these classifications (and the "loka") are only supposed to ever apply to our own personal experience is oversimplified. [Considering both internal and external phenomena makes one aware of the interconnectedness of our world, and is a powerful way of breaking down the concept of self.]
And I could also argue that whether or not one considers various things the Buddha speaks about as being "real" (or not) is not actually particularly important or interesting. [Perhaps sometimes they are, sometimes not?]
I would tend to argue that the really important
thing about all these analyses (aggregates, elements, sense bases) is that they are ways of drilling down into our experience in order to see through our conceptual trappings of self. If we take them as primarily a means to that liberation, delivered in various suttas to various audiences, at various times, worrying too much about consistency may well be a futile and pointless exercise. And certainly trying to construct a philosophical position out of the suttas seems to be a recipe for overcomplication and distraction.
I can't necessarily properly defend (or want to completely defend) the questions raised above, but I think they are questions worth asking.