Validation of the sources in the 30, 44, and 70 GHz channels. The top panel shows the cumulative completeness per flux-density bin of the PCCS2 catalogue. The lower panel shows the number of unidentified sources per flux-density bin. These sources have no clear counterpart in any of the external catalogues used for validation. However, many of these source have been detected in more than one Planck channel and this implies, first, that they could be real sources and not spurious, and one can consider the number of non-matched sources presented here as an upper limit. Second, the fact that they are not in the external catalogues suggests that, if real, they could be potentially interesting objects, maybe going through a flaring phase.