I am stuck on a diagram that shows the development of GDP over time period from '04 to '16. We have 4 graphs; actual GPD, and estimates of potential GDP made in '07, '10 and '15.

Now to the actual question. I am trying to understand why the different estimates for potential GDP differs in the earlier years. Why is the estimate made in 2015, when look ex. at the years 04 - 07, different than the estimate made in 2010.