Example spectra from our MC simulation compared to real SNe IIn and Ia-CSM. No effort has been made to fit the data, but the spectra were selected from our simulated sample based on their similarity to the observed spectra. The top two panels show a comparison with the Ia-CSM PTF10iuf that has good constraints on the spectroscopy epochs (Silverman et al. 2013). The early spectrum (−19d) is well fit with a 91T-like SN at −10 days with f_V = 0.67 and A_V = 0.71. Normal SNe Ia do not give an acceptable match. The spectrum at +3d continues being consistent with a 91T-like object. The phase of the underlying template is +20d and f_V = 0.27. The bottom panels show that simulated IIP-CSM SNe can provide good matches to several SNe IIn, such as SN 2005gl (Gal-Yam et al. 2007). The early, hot, spectrum of SN 2005gl is well reproduced by a SN IIP with f_V = 0.04 (T ~ 13 000 K). At this low f_V the spectral shape is not sensitive to the underlying type and any template could provide a hot SN IIn spectrum. At later times, however, when SN 2005gl develops clear Balmer lines, a SN IIP with f_V = 0.51 provides a remarkably good match.