Not surprisingly, the accuracy decreases with indicators for the "complexity" of the reaction, particularly with the inferred number of broken/formed bonds, the total number of substances in the reaction, and the number of boundaries. A similar trend is found for the number of different bonds and cycles after graph merging. In contrast, the performance does not depend systematically on the carbon imbalance |n + Cn - C |. The total number of compounds in a reaction exceeds 6 only in some entries in the Golden dataset since it also reports catalysts and solvents. This suggests that the performance declines with more fragments due to potential substance-matching misalignments. In some cases, no boundaries were detected in the MCS step. The lack of accuracy in the absence of a boundary strongly suggests to exit without success if no boundary is found, since the result is almost always wrong anyway. The details of this exploratory data analysis are summarized in Supplementary Fig. .