No doubt it is simplistic and incomplete, but also true that its estimates of
yearly average GISS approximate the end of year NASA summary months in advance, and track Gavin Schmidt's midyear projections very closely, so it must doing something right.
For example, when one uses the
yearly records for SOI and compares them with
yearly records of
GISS, there is ambiguity and uncertainty into where the
average is meant to be applied — is it the first of the year, or is it halfway through the year?