Location of the narrow Na I D absorption lines in SNe II (left), SESNe (middle), and SNe Ia (right panel). The names and phases with respect to the B-band maximum in their observed light curves are marked in each inset. Low-resolution spectra are presented in the top panels (pseudo-resolution – see Sect. 3 – of R_p = 1951, 3087 and 3869 from left to right), while higher-resolution spectra (R_p = 11 877, 9306 and 14 879 from left to right) are at the bottom. The vertical dashed lines indicate the position of the Na I D for the MW (cyan) and the host galaxy (magenta), with the integration window of ±1000 km s⁻¹ shown in shaded areas.