Stellar properties could be inferred incorrectly when assuming single star evolution if one does not consider the full multimodal posteriors. The main panel shows the χ² values for fitting our M = 3.5 M_⊙ mass-gainer model at X_c = 0.1 with our entire grid of single star models. The true and best-fit values are highlighted with lines. We add white contour lines at ${\chi }_{\text{best}}^2+1$ to highlight models that are statistically compatible with the true value. The side panels show marginal distributions (the minimum χ² marginalised over a given axis), where any values with ${\chi }_{\text{min}}^2\le {\chi }_{\text{best}}^2+1$ are filled with yellow to mark them as statistically compatible.