Spectral comparison between models and the selected sample of observations (see Table 2) at ~350 d (top panel), ~450 d (middle panel), and 800–1000 d (lower two panels). In each panel, we stacked models and observations in strengthening signs of interaction as we progress downwards. A distinct color is used for each SN while black is used for the models (see labels; light (dark) colors correspond to the original (smoothed) spectra). The galaxy lines were removed from the observed spectra, and the data were binned to reduce the noise.