a) Ratio of the intrinsic τ_V,   ISM derived by the model over the observed (attenuated spectrum) τ_V,   obs versus the τ_V,   obs. The dashed line is the one-to-one ratio. The red circles represent the early-type galaxies in HCGs, and the blue diamonds the late-type ones. b) Ratio of the intrinsic τ_V for stars in birth clouds, derived by the model over the observed τ_V,   obs versus the τ_V,   obs, using the same notation. We excluded 6 galaxies from the plot (HCG44a, HCG47a, HCG47b, HCG56b, HCG59a, and HCG68a) since their χ² of model-fit was more than 9.00 and the derived τ fairly uncertain (see Table 3).