Spectra of SN 2024iss at (a) −12, (b) 2, (c) 31, and (d) 69 days relative to V-band peak brightness compared with other well-studied SNe IIb at similar phases. Phases with respect to the V maximum are labeled. All spectra are shown in the rest frame and have been normalized. The vertical dashed lines mark the positions of certain spectral features at zero rest-frame velocity. For comparison, the gray curve underlying the spectrum of each comparison SN shows the shifted spectrum of SN 2024iss that matches their mean flux within the displayed wavelength range.