Official-source boundary
Launch records come only from governments, regulators, enacted legislation, central banks, exchanges, and recognized industry bodies. Aggregators can help discovery but cannot establish a date.
Evidence before coverage
The method is
the product.
Automation keeps ProvenDay watchful. Validation—not automation alone—decides what may become a published date.
Structured sources may auto-publish
The GOV.UK bank-holiday JSON feed is schema-checked, sanity-checked for complete division/year coverage, hashed, archived, and appended before it can replace the prior published snapshot.
Page changes create alerts, not dates
HTML pages from OPM, NYSE, ECB, SEC, and FINRA are checked daily. New content is archived, but a page-layout change cannot silently mutate the public calendar.
Rules have effective dates
The U.S. regular-way convention selects historical T+2 through 2024-05-27 and T+1 from 2024-05-28. Trade eligibility uses XNYS; settlement eligibility intersects XNYS and the U.S. federal calendar.
No estimates at the edge
Coverage is checked on every candidate date. If a requested year or calculation crosses an unverified boundary, ProvenDay returns an explicit error.
Publication law