There are two ways of assigning reaction roles to molecules found in ORD files, either relying on the labeling, or identifying reaction roles by considering the atom mapping of a reaction SMILES string. We found that relying on the labeling in ORD mislabels many spectator molecules as reactants, which explains the difference in reactant count distribution seen in Figure . Identifying the role of molecules in a reaction provides crucial context to machine learning models, adding domain knowledge to the data thereby improving performance. Atom mapping the reactions with the newest The role that a molecule plays in a reaction may more easily identified when only considering one reaction class at , since this allows the mechanistic details of the reaction class to be considered. Handling large and diverse datasets inevitably requires generalizations that may result in contradictions upon a more fine-grained inspection. In this work, solvents were separated from the other spectator molecules, because these can somewhat reliably be identified. Catalysts were not separated into their own category, since identifying catalysts is more subtle (especially with organocatalysis), and few reactions in the reaction string datasets contained transition metals.