NATO Neighbors

An attack on French Guiana would not trigger NATO to defend it, nor would attacks on any other french overseas territories except St Pierre and Miquelon off the coast of Canada. That also applies to other countries overseas territories, The Falklands War did not trigger a NATO response. Theoretically an attack on Hawaii would not trigger one either, assuming no mainland territories were attacked at the same time.

You're right. It's never "so simple" applying rules to every country, and edge cases can break down, but there is a roughly (roughly!) consistent distinction between things which are part of a country and things which are controlled by a country, which we'll often call territories.

Every country is slightly different, so New Caledonia's "exceptional status" is not exactly equivalent to a "crown dependency" of the UK or a "U.S. territory" or Niue's "free association". But it's convenient to make broad buckets to categorize thing and these are the buckets usually used on Jetpunk. We have to accept that no taxonomy will fit every piece of land perfectly and unambiguously and deal with it with common sense.