Accurate as far as I can tell to a century or in timescale. Comparing any past century averages to the past centuries increase does not provide a lot of data points. Comparing ice cores to CO2 measurements made other ways like in the atmosphere is silly.
I completely disagree.
I'm not sure what DE08 and DSS are, but all of the other points are from ice cores. The black line is the Mauna Loa atmospheric CO2 measurement curve.
This figure shows it a little better. There's another better one that I can't seem to find at the moment.