Top panels: H i mass distributions |$N_{\rm m}(M^{\prime }_{\rm HI})$| are constructed using the true values of integrated line flux and central frequency of each teams’ matches (joined circles). The redshift-dependent H i mass function (equation 15), from which truth catalogue sources were drawn, is multiplied by the comoving volume of the given redshift interval and plotted (grey curve). Black diamonds represent the H i mass distribution reconstructed using the full truth catalogue. Dotted lines indicate for each team the H i mass above which completeness exceeds 50 per cent. Bottom panels: The H i mass distribution residual represents the difference between the distribution constructed from the values of teams’ submissions and distribution constructed from truth values of teams’ matches. Both distributions are interpolated prior to finding the residual. Completeness values are in this case calculated using teams’ submitted values, and dotted and solid curves are used to delineate H i masses where completeness falls below and above 50 per cent, respectively.