Figure shows the distribution of unique components (elements/species) per structure in the dataset that has been curated for training the SkipSpecies vectors as described in Section II B. In Figure and b, the one-component materials come from polymorphs of H 2 and N 2 , which from the oxidation states route of the Materials Project , are automatically assigned oxidation states of 0+. From Figure , the mode number of unique elements in the dataset is three reflecting that ternary materials are the most frequent in this dataset though this is very closely followed by quaternary materials. This is reversed in Figure when we consider the unique species within the structures, where the most frequent number becomes four. This distribution shift arises from the presence of many mixed-valence compounds within this dataset. Further evidence of this is shown in that the maximum number of components when we consider species becomes ten, versus the case when we only consider the elements and would thus have at most nine component compounds.