Age–metallicity relation of the 17 galaxies that were removed from analysis in Section 4 due to the lack of linear metallicity gradient. The grey density map corresponds to the density of stellar particles that are currently bound and were born bound to the host galaxy. The colored density illustrates the density of our stellar disk sample (R < 15 kpc, R_birth < 15 kpc, |z_birth|< 1 kpc, |z|< 1 kpc, eccentricity < 0.5). The dashed lines show the merger events with a gas mass ratio > 25% (blue) and 10 − 25% (orange). Most of these galaxies are non-Milky Way-like due to too few disk stellar particles. The others are non-Milky Way-like due to a large spike in [Fe/H] in the inner kpc (e.g. subhalo 555601) causing a non-linear metallicity gradient (see also Figure 7).