Predicted gas-phase log(N/O) vs. log(O/H) + 12 abundance pattern in Galaxy A with failed SNe (light blue points; this work) and without failed SNe (orange points). The solid grey line corresponds to the average relation obtained from various observations by Dopita et al. (2016, see references therein), the grey points with error bars toa compilation of data of individual HII regions in blue diffuse dwarf galaxies (Berg et al. 2012; Izotov et al. 2012; James et al. 2015), and the dark grey crosses to Belfiore et al. (2017) from a sample of spatially resolved galaxies from the MaNGa survey.