Evolution with time of the abundance ratios of potential tracers of the progenitor metallicity in the optical epoch: solid black lines belong to Mn/Cr, dashed blue lines to V/Mn, and dotted red lines to Ti/Mn. For each couple of elements, the labeled curve is the one belonging to X(²²Ne) = 2.5 × 10^-4, whereas the other curve with the same type and color belongs to X(²²Ne) = 0.075. The dot-dashed green line shows the evolution of Ti/Cr ratio, which could be used as a control variable, see Sect. 7.