Residuals of the multiple-population properties δY (top), f_P1 (middle), and $\overline{Y}$ (bottom), obtained after subtracting the mass and metallicity trends, grouped by progenitor family. The dashed horizontal line marks zero residual, i.e. agreement with the global mass–metallicity relation; negative values indicate clusters lying below the predicted trend and do not correspond to unphysical negative helium enhancements (the physical δY is non-negative by construction). Boxes span the interquartile range, and horizontal lines mark the median. Individual clusters are shown as empty circles; filled points are the same clusters slightly shifted for visualisation.