Verification of the population-orbit method with mock data created from galaxies of the TNG50 simulation: TNG50 468590, TNG50 375073, TNG50 220596, and TNG50 2 from Panel (a) to Panel (d). For each galaxy, the left three plots show the distributions directly from the simulation, which are well matched by those extracted from the best fitting population-orbit models in the right three plots. From left to right, we show the distributions in phase space of the time-averaged radius, r, versus circularity, λ_z, of orbital probability density p(r, λ_z), age t(r, λ_z), and metallicity Z(λ_z, r), all shown only within 2 R_e. The dashed lines indicate our orbital-based division into four components: disk, bulge, warm component, and hot inner stellar halo. The corresponding mass fractions within a 2 R_e radius are listed in Table A.1.