Around 5500 molecules in the NMR8K dataset are annotated solely with experimental 13 C data, while 1 H and C chemical shifts are present for the remainder. H chemical shifts show greater sensitivity to the solvent used for experimental data collection, and while we had hoped solvent-induced variations in chemical shift could be captured during this next phase of model training, the identity of the solvent used was often lacking in our primary data. We were therefore forced to focus solely on the refinement of C predictions. We also had to disregard experimental data for structures with ambiguously defined stereochemistry. A more difficult task involves the removal of possible misassignments, for example where an experimental spectrum may be assigned to an incorrect structure or a chemical shift attributed to an incorrect atom. Since even a small fraction of anomalous training data can result in noticeable degradation of ML models, we adopted a cautious approach and rejected experimental data that was statistically at odds with our DFT calculations. A comparison of DFT and experimental C shifts (Fig. ) showed 911 values differing by > 10 ppm (1.6% of all DFT calculated shifts) and 10% of values differing by > 5 ppm.