Comparison between selected spectra of SN 2020nlb (in black) to various models. The red dashed lines show the ‘DDC15’ delayed detonation model and the blue dashed lines show the ‘PDDEL4’ pulsating delayed detonation model, both from Dessart et al. (2014). The green lines show the M_WD = 1.06 M_⊙ detonation model from Sim et al. (2010). The pre-maximum model spectral sequence of this model has high-cadence temporal sampling, so we co-add nearby epochs to increase the S/N. In these comparisons, we do not choose the best-matching spectra from the model sequence, but the spectrum taken nearest to the post-first light time of our data for SN 2020nlb. The time after first light (rather than time with respect to peak) of each SN 2020nlb spectrum is indicated.