Envelope mass-luminosity relation (panel a) and H-envelope base temperature-effective temperature relation (panel b) for Case B accretors. Single stars are shown for comparison and models with an average hydrogen mass fraction in their envelopes of ⟨X_env⟩_cc < 0.4 are marked. These stars may appear as BSGs at core collapse but their hot T_eff, cc is due to the low hydrogen content in their envelopes and not due to a thick convective hydrogen burning shell. Power-law fits are added and the dotted lines in panel b indicate log T_eff, cc/K = 3.9 and the transition base temperature at ${\mu }_{\mathrm{env},\mathrm{cc}}{M}_{\mathrm{env},\mathrm{cc}}/R_{\ast }\approx 0.02M_{\odot }{R}_{\odot }^{-1}$ where we find the BSG solutions. Cases B-e and B-l refer to early and late Case B accretors, respectively.