Data Overview. The data we have examined can be found in the QUESTDB dataset, which consists of 542 vertical excitations of small and midsize main-group molecules (molecules with 1-10 non-hydrogenic atoms). Of these excitations, 491 are from singlet ground states and 51 are from doublet ground states. Every excitation in the QUESTDB dataset is specified by its spatial and spin symmetries, and benchmark values are reported as "theoretical best estimates" (TBEs) calculated with a variety of high-level methods with the aug-cc-pVTZ basis. These TBEs have been used in this work to judge the errors of all computed excitation energies, even those obtained with a different basis set.