Type II supernovae as a distance indicator
The open supernova catalogue calculates absolute magnitudes from the observed apparent magnitude, luminosity distance and redshift decrements.  They note that they don't account for spectral energy distribution shape, so absolute magnitudes may be approximate if there is significant absorption by dust.
So the catalogue isn't recording a measured or modelled absolute magnitude derived independently of the distance, (which is required if the SN are used as standard candles), but a calculated absolute magnitude derived from the apparent magnitude and the redshift.