In this work, experiment and theory have combined to elucidate the complex nonlinear spectroscopy of short-lived, autoionizing Rydberg states located between 17.3 -18.1 eV in the polyatomic greenhouse gas, CO2. Experimentally, attosecond XUV FWM spectroscopy, a recently developed nonlinear technique that utilizes a noncollinear beam geometry between a short train of subfemtosecond XUV pulses and two few-cycle NIR pulses, generates background-free FWM ] dark state as the best candidate to mediate the wave-mixing process, the oscillator strengths of transitions between all states potentially involved in resonant FWM pathways were calculated to rationalize the dominance of the Henning diffuse states in transient wave-mixing measurements. Large ground to diffuse state oscillator strengths combined with substantial oscillator strength transitions between the dark state and the Henning sharp states result in the selection of pathways characterized by an initial XUV excitation to Henning diffuse states, but emission from the Henning sharp states. Consistent with the reported experimental lifetimes, these pathways generate FWM signals that encode the lifetimes of the Henning diffuse states in the FWM emissions of the sharp states. This work broadly demonstrates that, with the correct set of coupling strengths, the properties of short-lived, spectrally broad features can be successfully measured using emission from more spectrally narrow resonances, reducing the impact of spectral congestion. Therefore, these results not only provide insights into the decay dynamics of autoionization states in a highly significant polyatomic molecule, but also illustrate a powerful application of experimental and theoretical attosecond XUV FWM analysis that can be utilized in more complex chemical systems. Calculations of linewidths and corresponding lifetimes of Henning diffuse and Henning sharp series for the n = 6 -8 and n = 5 -7 states, respectively, compared with experimentally measured lifetimes. Also, the computed data for the dark state is given.