Figure shows the predictions of the SISSO models selected based on considerations of cost and accuracy as a function of the GW +BSE reference values of the singlet exciton energy (optical gap). Parity plots for all other SISSO models are provided in the ESI. Overall the model predictions are quite close to the reference values. The low-cost model M 1,3 has a few outliers with larger deviations from the reference values. Typically, the outliers tend to be systems that are somewhat chemically distinct from the majority of systems in the dataset. One example is 2-(Naphthalen-2-yl)azulene (CSD reference code PUJQIV), which contains a 7-membered ring fused with a 5-membered ring. Biphenyl (CSD reference code BIPHEN) and terphenyl (CSD reference code TERPHE02) comprise benzene rings connected by single bonds, rather than the large aromatic systems of fused rings characteristic of most of the PAH101 set. For biphenyl in particular the optical gap value of 3.41 eV included in the PAH101 dataset 110 is a significant underestimation compared to the experimental values of 4.1-4.18 eV. Therefore, it could be argued that this data point is less reliable and the model prediction is in fact closer to experiment. Coronene (CSD reference code CORONE01) and 9,18-diphenyltetrabenz(a,c,h,j)anthracene (CSD reference code FACPEE) do not appear chemically or structurally distinct from most of the materials in the PAH101 set, however they have unusually high values for the crystal triplet formation energies, E C T , which may explain why their optical gaps are overestimated by M 1,3 . For most of the M 1,3 outliers the predictions of the intermediate-cost M 3,3 &M 4,2 and higher-cost M 4,3 models are closer to the reference values, with the exception of terphenyl, which remains an outlier. Based on this, the third stage screening with M 4,3 is not beneficial and we would suggest a two-stage workflow with thresholds defined depending on one's tolerance for false positives. We also note that the optical gaps obtained from GW +BSE are typically within 0.2 eV from experiment. The training RMSE values of M 1,3 and M 3,3 &M 4,2 are 0.16 eV and 0.11 eV, respectively. Therefore, it may be reasonable to set n=2 to account for the errors of GW +BSE on top of the errors of the ML models.