So with the ESRL data, I subtract the mean of the respective months of 1994-2013 from the overall monthly totals, and compare with the monthly averages I post. Here is a table of discrepancies for 2015, in the monthly anomalies, in °C
Mostly it is accurate to 3 sig figs. The exception is February, which also stands out in 2014. I think the reason is the treatment of leap years. With ESRL I subtracted the means of all Februaries in the base from the monthly means, while in my posting method, I form anomalies for each date first, abd then average to get the month. So in effect, for 2015 I compare with the average of all periods Feb1-28. Both ways are reasonable, and the difference is small.
AFAIK, there is no published global average of daily anomalies, so I will keep doing it the way I do. But it is useful to have the check of the monthly averages, and also to know that there is such little difference between surface and sig995.
I'm currently dealing with change of year issues - I'm restructuring the whole posting calculation to make it less year-dependent. Numbers for 2016 should appear soon.