Two examples of the evolution of $\widehat{[\mathrm{Fe}/\mathrm{H}]}(R_{\mathrm{birth}}$ = 0 kpc, τ) after a merger with pre-enriched gas. Due to the metal-rich spike in the galactic center (Figure 7), we remove the inner kpc for visualization purposes. The subhalo in the top row (subhalo 554523) had a major merger at lookback time ∼9 Gyr ago which brought in more metal-rich gas and increased the metallicity of the entire disk. This allowed for the projected central metallicity (marked with the red “x”) to also increase. The subhalo in the bottom row (subhalo 514829) experienced a metal-rich merger ∼8 Gyr ago. However, instead of increasing the metallicity throughout the entire disk like in the top row, here only the outer disk had an increase in [Fe/H]. This thus weakened the metallicity gradient, and in turn lowered the projected central metallicity. These examples show that even something as trivial as the metallicity of the merger compared to the main galaxy cannot begin to disentangle when $\widehat{[\mathrm{Fe}/\mathrm{H}]}(R_{\mathrm{birth}}$ = 0 kpc, τ) increases or decreases after a merger.