Normalized SSD evolution of a single model galaxy for differing choices of the age bins used to define the young and intermediate-age populations. All curves are normalised so as the SSD_norm value is exactly zero at t_sim = 1250 Myr. The fiducial values are < 200 Myr and 200–400 Myr respectively (dark green line in all panels). In all cases, the model galaxy is subjected to ram pressure (equivalent to RP-fid) that begins to affect the SSD value at t_sim = 1250 Myr. Left panel: Young stars defined as < 50Myr instead of < 200Myr. Middle panel: Definition of the intermediate-age bin is varied from 200-400 Myr up to 1000–1500 Myr (see legend in that panel). Right panel: The pink line is the SSD for a young population with age < 50 Myr and an intermediate-age population with age < 300 Myr. These two age bins are no longer exclusive (i.e., young stars are found in the intermediate-age bin).