The longer token length molecules are longer than "a missing word" under the definition of the MLM. It fits better with another application of the BERT transformer model, the next sentence prediction, which predicts the entire next sentence based on the previous context. This could be an area of exploration for future prediction of longer molecules. However, this has not been implemented in this paper, since the low model predictability of longer molecules would not significantly affect the ChemMLM's ability to complete reactions. The missing molecules in an incomplete reaction are commonly the side reactants and side products, which are usually smaller molecules. Table also shows the ChemMLM models do not show significant difference in prediction of hidden molecules between the LHS and RHS, in terms of their correction rate of short, middle and long token length molecules. This is because the models were trained using a dynamic mask method, which learned the semantics at two sides of the reactions simultaneously. However, the ChemMLM model trained from USPTO data shows better model performance in test data compared with the current ChemMLM model learned from the combined data. Perhaps a finetuned ChemMLM model learned from the larger reaction dataset could increase correct prediction rate in the test dataset, but the ChemMLM learned from the USPTO reactions were sufficiently predictive to predict the short and middle length hidden molecules. This indicates that the USPTO reaction dataset is capable to provide comprehensive types of complete reactions for the ChemMLM model to learn from. The ChemMLM model in the rest of this paper is referred to the ChemMLM trained from the USPTO reaction only. benzene proposed by ChemBalancer, the updated reaction could be materially balanced with stoichiometric coefficients. These false positive complete reactions were caused only in very rare situations. This happens when some of the 333 enumerations to predict the missing molecules by ChemMLM were not semantically meaningful but their SMILES syntax was valid. This prediction remains valid only when the updated reactions were possible to be balanced by large values of stoichiometric coefficients in coincidence.