> in fact there is already no common international agreement about where a nation's boundary extends to in the z-axis. The observed limit is "however high that country can detect and shoot something down"

That's the thing though, if you use that definition then 99.9+% of them are fair game, because _only_ ones around equator at a specific height are at a fixed point. Otherwise they migrate a lot and what country they're over would depend on what second you look.