In our QSGW study of CO on Pt (111) and Cu (111), we were able to resolve key spectral features of deeper states below the Fermi energy and qualify CO site contributions to the LUMO 2π* at various coverages. While previous studies could partially capture some of the states, they often utilized HSE or DFT+U methods, which require manipulation of either Hartree-Fock exchange in HSE or the U value in DFT+U in order to match experiment. Essentially, an answer must be known beforehand to set adjustable parameters. QSGW-level calculations appear to accurately explain available observations of CO on Pt (111) and Cu (111) without model assumptions or free parameters, including detailed spectral features from photoelectron and photoemission experiments. Resolving the puzzle of CO adsorption on transition metals required both self-consistent GW-level calculations and an interfacial model that include the permutations of sites and coverages that may be possibly realized. Since CO is a key reaction intermediate and product in CO2 reduction to valuable C2+ products, interest remains high in increasing the selectivity and activity through electrochemistry and plasmonic means of catalysis. This study acts as a stepping stone to a comprehensive understanding of CO2 reduction. Self-consistent GW calculations can potentially elucidate other CO-related intermediates key to the reduction process, identifying spectral features related to the facet-dependence of reactivity. Looking forward, RPA total energy from LDA-based eigenfunctions seem to significantly improve energetics relative to common DFT functionals for these systems. Since that work constructed the total energy from DFT eigenfunctions, which from the Bader analysis we cannot expect it to be reliable, RPA total energy from QSGW should be significantly better. In QSGW the path of adiabatic connection bridging the noninteracting Hamiltonian to the interacting one is better than the path given by Kohn-Sham theory, by its construction. Thus QSGW-based RPA total energy should be another powerful tool to resolve and predict reaction enthalpies.