Supplementary Data and Reproducible Calculation Package

Supplementary data and reproducible calculations for the manuscript “Off-Exchange Migration and the Limits of AI Attribution: A Data Synthesis of Venue Composition, Execution Quality, and Enforcement in U.S. Equity Markets, 2019 to 2025” (NSRI submission NSRI-J-2026-0126). This deposit contains six compiled CSV datasets (S1–S6), a seven-sheet calculation workbook (S7), a README/data dictionary, and a provenance ledger. The files document the public sources, calculations, and limitations behind the manuscript’s analysis of off-exchange trading, execution quality, and enforcement. The workbook includes live formulas and robustness checks to support reproduction of the reported results. This record is the supplementary data package, not the manuscript itself.