Histograms showing the luminous mass distribution of precursor galaxies at z_ini = 3 that contribute at least 5% to the final mass of either the first-ranked group galaxy m₁ (solid magenta lines) or the IGL (solid black lines), with median values indicated by vertical dot-dashed and dashed lines, respectively. The distributions are shown separately for each group class: single-BGG (left), double-BGG (middle), and non-BGG (right) panels.