Left panel: cluster counts of PSZ1-North sources as a function of the SZ S/N detection. The PSZ1-Val sample is represented in green, which includes SZ validated sources in all previous follow-up programmes. The confirmed clusters within the ITP13 sample are shown in blue, whereas non-validated clusters (classified as Flag=3 and ND) are shown in red. Right panel: fraction of confirmed clusters as a function of the S/N in the PSZ1-North sample. The red line represents the purity at the moment of the publication of the PSZ1 catalogue and blue line shows the purity after completing the ITP13 follow-up. The orange line represents the accumulated purity of the full PSZ1 catalogue at the moment of its first publication, while the black dashed line is the predicted PSZ1 reliability retrived from Planck Collaboration XXIX (2014) (see Fig. 10 therein).