There are lots of familiar names behind this new paper in JAMS - Rutherford, Mann, Wahl and Ammann. It seems that their infilling RegEm methodology has received some criticism. Apparently though, it "doesn't matter".
Smerdon et al., (2010) report two errors in the climate model grid data used in previous pseudoproxy-based climate reconstruction experiments that do not impact the main conclusions of those works (Mann et al., 2005; 2007a). The errors did not occur in subsequent works (Mann et al., 2009, Rutherford et al., 2010, and Schmidt et al., 2011) and therefore have no impact on the results presented therein. Results presented here for the CSM model using multiple pseudoproxy noise realizations show that the quantitative differences between the incorect and corrected results are within the expected variability of the noise realizations. It should also be made clear that the climate reconstruction method used in Smerdon et al. (2010) to illustrate the nature of the errors, RegEM-Ridge, is known to produce climate reconstructions with considerable variance loss and has been superseded by RegEM-TTLS in Mann et al. (2007) and subsequent works.