Difference between literature and GSP-Spec open cluster metallicities (computed as the mean [M/H] of their member) for OC with at least one cerium abundance. Blue, green, and red points indicate the number of stars belonging to each OC (one, two, or more than two members, respectively). The two horizontal lines at ±0.15 dex indicate the OC with good metallicities that are kept for further analysis.