Cluster distribution in the mass-redshift plane. Filled points: Clusters identified by the Planck all-sky survey. Empty boxes: Clusters from the SPT collaboration. Empty triangles: Clusters from the ACT survey. Masses in the Planck catalogue were derived iteratively from the M₅₀₀–Y_SZ relation calibrated using hydrostatic masses from XMM-Newton. They were not corrected for the hydrostatic equilibrium (HE) bias. Published SPT masses were estimated ‘true’ mass and were re-normalised by a factor of 0.8 to the Planck standard for comparison. The confirmed cluster studied in this work is shown using a red cross. The blue shaded box identifies a region of massive clusters, M₅₀₀ >  5 × 10¹⁴M_⊙, at z >  0.7 which is poorly populated. There are ∼25 objects in this region as found by all the SZ surveys. The green and blue dashed lines indicate the 20% and 80% survey completeness contours, respectively, of the Planck SZ release 2 (PSZ2) catalogue which are shown in Fig. 26 of Planck Collaboration XXVII (2016).