One source of uncertainty in our dataset is the quality of our assessment of "synthesizable or not." The QM9 dataset should involve well-studied areas of chemical and structural space because it focuses on small molecules, which have relatively few isomers. We test this hypothesis by evaluating E min 's accuracy for predicting synthesizability as a function of the number of heavy atoms in each molecule, shown in supplemental ??. One may argue that molecules with more heavy atoms (and thus more isomers) are less likely to be well-studied, thus accuracy may fall when plotted against increasing number of heavy atoms. However, we find negligible differences in E min accuracy on molecules with 6, 7, 8, and 9 heavy atoms. Therefore, we are confident our reported/unreported labels sufficiently capture each molecule's true synthesizability.