Evolution of the expansion velocities measured from Fe iiλ5169 for SN 2012bz and six GRB-SNe of low (diamonds) and high-luminosity GRBs (boxes) with good spectroscopic data. Measurements were performed on our data as well as on the spectra of Patat et al. (2001), Hjorth et al. (2003), Malesani et al. (2004), Pian et al. (2006), and Bufano et al. (2012). The value of SN 2013cq was taken from Xu et al. (2013). The grey-shaded area displays the interval of observed GRB-SN peak times.