As discussed above, measurement of the ultrafast lifetimes of the Henning diffuse states is a direct consequence of the resonance-enhanced nonlinear technique used to probe these Rydberg state dynamics of CO2. The transitions that comprise each interaction of the FWM scheme work in concert to regulate the emission intensity of individual pathways, selectively enhancing some emission signals relative to others. Favorable pathways are selected not only by the photoabsorption cross section of the state accessed by the XUV pulse, but also by additional NIR transitions between bright and dark states. Thus, attosecond XUV FWM spectroscopy permits the investigation of states that give rise to less prominent features or are obscured by spectral congestion in the linear absorption spectrum. For example, despite less-than-ideal spectral resolution, the oscillator strengths of the FWM interactions in CO2 operate such that the shortlived, and therefore spectrally broad, Henning diffuse states emit primarily from spectrally narrow Henning sharp states without significant contamination from a long-lived emission component. Although incidental in this system, the results illustrate that, with careful consideration of intermediary dark states and transition oscillator strengths, attosecond XUV FWM spectroscopy coupled with theory can be successfully utilized to emphasize the dynamic signatures from otherwise poorly accessible states.