At this point it is worth revisiting the training set, both experimentally and in terms of theory performance. The latter is limited to those submissions which have provided training performance data. As the training set also included cases with a proven or speculated higher-order anharmonic resonance which shifts around the O-H stretching energy levels by up to ±10 cm -1 , one can now check whether submissions without regression step fit better the raw or the deperturbed experimental data, to learn more about the impact of this resonance. Finally, one can check whether a method performs better for the training set than for the test set or more or less equally well for both. Because the spread of wavenumber values turned out to be quite similar for the test and training data set, a balanced performance would not be too surprising.