Refs. 11, 12, and 13 introduced the CVS-0 approach, which simply substitutes Ĥ with the CVS-0 Hamiltonian ( Ĥcore ) in Eq. ( ). Thus, the X-ray response wave functions are computed within the configuration space of coreexcited determinants only, leading to convergent solutions. Note that, in contrast to Ref. 13, Refs. 11 and 12 use a different nomenclature and refer to Ĥcore as the CVS-CC-RSP and fc-CVS-EOM-CC Hamiltonian, respectively. The use of the CVS-0 Hamiltonian effectively replaces the sum over all states in the EOM-CC expectation-value approach for computing 2P moments with a sum over just the core-excited states; the contribution of valenceexcited states to the SOS moments is omitted. This is justified for most RIXS transitions for which the dominant contribution to the moments arises from nearly resonant core-excited states. However, in contrast to RIXS, in X2PA, the core-excitation energies can be significantly different from the energies of the two absorbed photons. In such cases, it is reasonable to assume that the near-resonance contribution can arise from not only the core-excited states but also from low-lying and high-lying valence states. For such cases, the CVS-0 approach would miss important contributions to the X2PA moments; therefore, approaches that can include the valence contribution are desirable.