Partial spectra of SN 2016jbu (Brennan et al. 2022a), SN 2015bh (Thöne et al. 2017), and SN 2010mc (Ofek et al. 2013a) during event B rise phase. A flash ionisation feature is seen around 4700 Å in the −14, −13, and −11 d spectra of SN 2016jbu, in the −9, −6, −5, −3, and −1 d spectra of SN 2015bh, and in the −12 d spectrum of SN 2010mc. The −6 d spectrum of SN 2016cvk is included for comparison. The locations of the N III, C III, and He II lines at 4641, 4650, and 4686 Å, respectively, are indicated with red dashed lines. Fluxes have been normalised by dividing the spectra with a continuum estimated based on the line-free regions between 4500 to 9000 Å.