Scatter plots of the formation times (top) and metallicities (bottom) derived from the OptExt (x-axis) and the R50 (y-axis) for the INSPIRE DR1 objects, which are colour coded according to their relic class (Sect. 7.2). In all panels, we always plot the mean between the values obtained with REG = 0 and with the MAX_REGUL, and show the one-to-one line (dashed black). The bins in the histograms are chosen to be as similar as possible to the uncertainties on the relative quantities.