We investigate the impact of a late-time transition in the standardized absolute magnitude $M$ on the best-fit values of cosmological parameters using the $\mathrm{Pantheon}+\mathrm{dataset}$. Extending previous analyses which focused on flat $\mathrm{\Lambda }\mathrm{CDM}$, we examine this transition within flat $\mathrm{\Lambda }\mathrm{CDM}$ (Lambda Cold Dark Matter), wCDM (cold dark matter with a constant dark energy equation of state w), and CPL (Chevallier-Polarski-Linder) cosmologies as well as a model-independent cosmographic expansion, employing both frequentist (${\chi }^2$ minimization with Akaike Information Criterion/Bayesian Information Criterion) and Bayesian (Markov-chain Monte Carlo and nested sampling) inference frameworks. We confirm that the data consistently favor a step in absolute magnitude of $\mathrm{\Delta }M\simeq 0.19\mathrm{mag}$ at a characteristic distance of $d_{\mathrm{crit}}\approx 20\mathrm{Mpc}$. The inclusion of this transition leads to a statistically significant improvement in the quality of fit and has a distinct impact on parameter estimation: it induces a systematic increase in the inferred Hubble constant of approximately 2% across all tested models. In contrast, we find that the dynamical parameters governing the background expansion, including the matter density ${\mathrm{\Omega }}_m$ and the dark energy equation of state ($w_0,w_a$), remain stable and largely unaffected. These results indicate that the 20 Mpc feature acts primarily as a low-redshift calibration shift rather than a modification of the late-time expansion history.

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• Cosmological parameters
• Evolution of the Universe