The method AMD is using to determine TDP is unknown:
TDP. Thermal Design Power. The thermal design power is the maximum power a processor can
draw for a thermally significant period while running commercially useful software. The
constraining conditions for TDP are specified in the notes in the thermal and power tables.
http://www.amd.com/us-en/assets/cont...docs/33954.pdf, page 10

In order to know their method we need to know the following two variables:
1) thermally significant period
2) commercially useful software