Extending recent analyses using PISA data, the current study utilises the OECD's Survey of Adult Skills (PIAAC) to test the central claims of knowledge capital theory. PIAAC has a distinct advantage over PISA in that it more directly tests levels of purported 'knowledge capital' across an entire national workforce, rather than offering approximations based on the performance of 15-year-old students. Findings from our two original studies reported herein further refute the tight linkage between cognitive levels and GDP growth per capita envisaged by proponents of knowledge capital, most notably the OECD and World Bank. These results suggest that knowledge capital theory is now degenerate. If scholars are willing to extend this reporting of results refuting knowledge capital theory, this will likely accelerate the theory's loss of momentum in the coming years.