Stress Testing Observer Normalized Coherence in Disk Galaxies Distance, Radius, and Surface Brightness Robustness using SPARC

Recent analysis of disk galaxy dynamics using the SPARC sample, reported in Observer-Normalized Scale Relativity: Coherence Constraints on Global Physical Inference and Disk Galaxy Dynamics (DOI: 10.5281/zenodo.18283964), has shown that an acceleration-domain normalization exhibits substantially reduced scatter relative to density-based formulations, particularly when galaxies are grouped by intrinsic morphology. To assess whether this coherence reflects a genuine physical regularity or instead arises from correlated variables, catalog conventions, or observational systematics, this work performs a sequence of targeted stress tests designed explicitly to dismantle the observed correlation. We test sensitivity to distance covariance, radius definition, and residual dependence on surface brightness. We find that the coherence survives all three tests. Residual structure is traced to effective surface brightness, which acts as a secondary normalization axis. Incorporating this correction further reduces scatter without introducing new systematics, indicating that the observed coherence is not a bookkeeping artifact but an incomplete normalization. This record includes explicit links to the associated stress-testing analyses, datasets, and computational notebooks supporting the reported results, clarifying the methodological lineage of this work. Version note: Version 2 adds Appendix A (Framework Scope and Admissibility Constraints). All analyses and results are unchanged.