Comparison between ⟨t_★, B⟩_ℳ (panel a) and ⟨Z_★, B⟩_ℳ (panel b) for the bulges of the reference sample (135 CALIFA disk galaxies) derived using STARLIGHT (Z4 library). The x-axis shows results obtained when partially including the UV regime (4000–4750 Å), while the y-axis displays the results when excluding it (both have spectral coverage extending to 6800 Å). While stellar age estimates remain consistent, stellar metallicity tends to increase when this wavelength range is omitted. This systematic shift may explain why some metallicity assessments from MUSE data (which totally lack the UV regime) yield higher values compared to the reference sample.