Comparison of the [Fe/H] predicted by this work and by three literature ML catalogs with the PASTEL (top row) and SAGA (bottom row) databases. Our results are shown in the leftmost plots, where the grey points show the results before, and the purple ones after, augmenting the reference SoS-Spectro catalog with very metal-poor stars. The median [Fe/H] differences for the before and after augmentation samples (computed only for [Fe/H] < −2) are indicated in the top-left corner of the first plot in each row. A similar comparison is presented for the following catalogs: Andrae et al. (2023, blue, center-left panels), Gu et al. (2025, red, center-right panels), and Zhang et al. (2023, green, rightmost panels).