The absolute error of the true-z distribution estimated by different amount of spec-z bin data. Upper panel: ${\displaystyle \sum _i}|{\widehat{P}}_{ij\prime }-P_{ij\prime }^{\mathrm{true}}|$, the absolute difference between the true-z distribution measured from the mock, P_ij′^true and the one estimated, ${\widehat{P}}_{ij\prime }$. Lower panel: ${\displaystyle \sum _i}|{\widehat{P}}_{ij\prime }-P_{ij\prime }^{\mathrm{true}}|/{\sigma }_{P_{ij\prime }}$ the absolute difference normalized by the estimated error σ_Pij′. In both panels, the results from full spec-z data (blue), no spec-z bin 9 and 10 (red), no spec-z bin 7 to 10 (violet), and SC only (orange) are compared. With the reduction of the number of spec-z bin data, the constraining power is weakened. When only the high-z spec-z bins are missing, the impact is mainly localized in the high-z tomographic bins with the low-z bins little affected.