Left plot: mean number of faint galaxies in fossils (solid lines) and controls (dashed lines) as a function of redshift. The upper panel shows the evolution observed in groups defined using the ΔM₁₂ criterion, while lower panel corresponds to groups identified according to the ΔM₁₄ criterion. Error bars are computed using the bootstrap resampling technique. The inset panels show the ratio between the mean number of faint galaxies in fossil and control groups. Right plot: mean number of faint galaxies classified as new members (upper panels) or lost members (lower panels). Error bars are computed using the error propagation formula.