The PDF doesn't have all the data that the chart shows. There's only six quartly data points the others are annual and averages. Where did the data for that chart come from?
I expect Stuart used the annual averages and then quarterly averages.  Nothing wrong with that, just the resolution gets higher to the right hand side of the graph.
I made my own.  Did my own data extract from the first table in the PDF.

http://peakoil.com/post204693.html#204693

Correct - I just took the data right off the Petroleum Review article and plotted each point at the midpoint of the corresponding period (so 7/1 for years, and 2/15 for first quarer etc. It looked too busy with the symbols in so I took them out, or that would be clearer.