Left: multiepoch spectra (at 100, 150, 200, 250, and 300 d after explosion) for the SN Ia model DDC15 with a stripped-material mass M_st of 0.18 M_⊙. Right: same as left, but for the model DDC15 at 200 d and for a range of stripped material mass of 0.0018, 0.017, 0.059, 0.12, 0.18, and 0.58 M_⊙. In a qualitative sense, time and M_st have a similar impact on the optical spectrum, with a strengthening of the Hα line relative to other spectral features with either time or M_st. Quantitatively, the correspondence does not hold since the bolometric luminosity changes significantly with time but only weakly with M_st at a given time.