Crab nebula polarization flux SED as obtained from Planck LFI (Planck Collaboration XXVI 2016), Planck HFI data reanalysed from the maps soon published in Planck Collaboration III (2018), WMAP (Weiland et al. 2011), XPOL (Aumont et al. 2010), POLKA (Wiesemeyer et al. 2014), and NIKA (this paper) data. NIKA and POLKA values are estimated over the entire extent of the source. The best-fit models and the data both account for the Crab nebula fading with time, using 2018 as year of reference. We also show the single power law best-fit model in cyan.