Indeed, we are in the position to address the reliability of commonly adopted all-electron quantum chemical calculations, while validating at the same time our approach. As for 2T-N and 2T-7N, all-electron calculations are typically truncated to single and double electronic CIs. Among them, we mention CIS(D), an approach that accounts for single CI, and introduces double CI perturbatively, spin-component-scaled second order coupled cluster (SCS-CC2), spin-component-scaled second order algebraic diagrammatic construction (SCS-ADC(2)), 2,3,7,56 double-hybrid DFT and DFT multireference configuration interaction (DFT-MRCI). All these approaches confirm the important role played by double CI to properly describe the ST inversion. However, the fast increase in the number of multiple CI precludes higher order studies using all-electron wavefunction-or density-based approaches.