Probability distribution of the surface helium mass fraction (left three panels) and surface nitrogen mass fraction enhancement factors (right three panels) of the donor vs the accretor for different ranges of accretor masses during the semi-detached phase: below 20 M_⊙ (top panels), 20-30 M_⊙ (middle panels) and above 30 M_⊙ (bottom panels). The different coloured stars symbols with error bars denote the positions of the semi-detached systems from the TMBM survey (Mahy et al. 2020a,b). The orange line indicates where the donor and accretor abundances are the same. The grey-scale gives the probability fraction in each pixel. The total probability is normalised such that the sum over the entire area equals unity.