[M/H] abundance distributions of member stars per cluster for the GSP-Spec Matisse-Gauguin algorithm (astrophysical_parameters.mh_gspspec) before and after recommended adjustements (see Sect. 3.2.1) The clusters are ordered by ascending [M/H] literature values (the lowest values to the left). These literature values are given by the black triangles. Cantat-Gaudin et al. (2020) provided the cluster members. Marks indicate the median of the distributions, and shaded regions indicate the 68% and 98% intervals. Numbers at the bottom indicate how many estimates were available to represent the distribution. Ideally, all predictions are within a small interval, which agrees with the triangles. We did not filter the estimates using the flags to keep enough stars per cluster, but nevertheless, the agreement is remarkable.