I don't know how they did their averaging
An appeal to ignorance? (I have learned something from this discussion.)
Regarding the MWP. The best I can do right now is to refer you to
this document. I will note that it is not a peer reviewed paper however in the figure it shows 4 reconstructions of Northern hemisphere temperature (the solid lines). The reconstructions are from peer reviewed journals. Each reconstruction used a different set of proxy data (although there may have been some overlap), different methodologies and different authors. Go wild!
I took a look at the Mann paper and then started looking for the papers he refers to. In the process of searching, I found this data: ftp.ngdc.noaa.gov/paleo/contributions_by_author which has some of the "raw" data used by those authors. I say "raw" because the proxy data has been tinkered with in various ways.
I have looked at 3 so far, jones1998 shows warming anomalies in both hemis from 1960 onwards but the readme says that the 1961-1990 anomalies have been altered in a way I don't understand (yet).
Crowley2000 is also mentioned in Mann's paper and has data that has been thoroughly manipulated using a simulation to remove all forcing effects except those from greenhouse gases. There's no testing of the CO2 forcing hypothesis and therefore no proof of anything.
Evans2002 (mentioned by Soon) only goes back into the LIA, but shows many warmer decades than any in the 1900's. Unfortunately this is based on tree rings and there's no indication of the method used to determine temperature.
I have a lot more work to do, but so far the hockey stick looks like an artifact of assumptions and methodology and is not supported by the raw data.