Na I D violin plots of the Na I D EW evolution for each SN type (from top to bottom: SNe II, SNe Ia, SESNe, and SNe-int) showing the mean and extreme of the distribution (white point in the box and edges of central vertical lines) and a kernel density probability estimation (coloured area). The number of SNe within each distribution at each epoch is indicated above each bin. We require at least two spectra per SN in intervals of 15 days for stacked EW measurements.