Comparisons of stellar parameters between GSP-Spec and a high-resolution spectroscopic study of VMP stars by Li et al. (2022). (Top) Comparison of the metallicities from optical high-resolution spectroscopy with the GSP-Spec metallicity for VMP stars from Li et al. (2022). (Bottom) Relation between T_eff and [Fe/H] discrepancies. The orange points show stars that satisfy the filters introduced by Recio-Blanco et al. (2023) for constructing the metallicity distribution function.