Crawford Speed of Light PRL v1.2

The primary data supporting the findings of this study are presented in Tables \ref{tab:track1} and \ref{tab:track2}. Track 1 data consist of vacuum density estimates for cosmic structures, compiled from observational literature. Track 2 data are a subset of the publicly available Pantheon+ Type Ia supernova dataset \cite{Scolnic2022}, accessible via the original publication. Additional resources, including detailed derivations and supplementary materials, are available on the OSF project page: \url{https://osf.io/f2r7d/?view_only=9d70b72857b24e939163687d7b44ff7c}.