What does the 'version' grid refer to in the GHCN/V2/adjusted/mean/temp dataset?

I would suggest that you look at the following overview of the GHCN:


From what I understand, there are many different ways to calculate monthly mean temperature. The GHCN project decided to include data from many different sources, each of which might have calculated monthly mean temperature in a different way and the resulting time series for monthly mean temperature were designated with different version numbers. Based on what I read in the temperature data readme file at the GHCN ftp site, the lowest version number is given to the longest time series of data, the next highest version number is given to the second-longest time series, etc.

-- Michael Bell