Well, NSE are quite adequate in representing the mean features of the flow. One may argue that there is feedback from smaller-to-bigger scales (backscattering), which there is, but in principle such feedback is ignored in industrial CFD. Judging adequacy is loosely based in integral principles for a certain flow archetype, rather than an exact evaluation of the fields obtained. That is, you go and check mean + modelled features and compare these with integral quantities (Strouhal, Nusselt, correlations, integral times). A more "serious" verification may involve checking the turbulence cascade via energy power spectrum, and see whether LES is at least representing accurate decay in the phase space.