Would you know who first measured the 2K race walk course just outside the stadium? That 9-loop course started and finished in the stadium. It was first used for the IAAF race-walking challenge in April 2008 -- before the stadium was completed. Since the Marathon course crossed the race walk course, I would imagine some of the measurements from the race walk course may have been used.
The carpet on the race walk course, that Dave refers to in his report, is actually the 4-millimeter thick synthetic Mondo used for track surfaces. The 4 meter wide Mondo synthetic surface was added after the granite surface raised concerns following the IAAF Walk Challenge. That may have been the most expensive race walk course ever built.