Is M_B really a constant?

M_B is the Supernova absolute magnitude. Ref. [1] isolates the distance ladder d_L(z) from the Baryon Acoustic Oscillations (BAO) and from the Type Ia supernova data to determine M_B. The degeneracy between the absolute magnitude and the Hubble constant H₀ for the supernova data is replaced by a degeneracy between M_B and the sound horizon r_d. Since the data is for certain redshifts, the Gaussian processes (GP) regression extrapolates the values for the whole redshift range. By canceling the distance ladder, the GP gives M_B = −19.25 ± 0.39 as a mean for the full distribution when using the sound horizon from late time measurements. The estimations provide up to 1 σ possibility of a nuisance parameter presence δM_B(z) at higher redshifts.