Comparison between MCXC-II redshifts and spectroscopic redshift values from SDSS-based catalogues. The revised values discussed in Sect. 3 are marked in red, and connected to the MCXC-I values by a red line. Left panel: comparison with the closest potential counterpart from the Wen & Han (2015, WH) catalogue (see text). MCXC J0019.6+2517, labelled in the figure, is a line-of-sight structure where the main component is identified with the richest second-closest WH cluster. Right panel: same for redMaPPer clusters from the updated version of the catalogue of Rozo et al. (2015), published by Rykoff et al. (2016).