Document vault

The project keeps a private copy of every exhibit's source and publishes the SHA-256 hash of what the address served on the fetch date. If a page changes or disappears, the hash shows whether the document cited is the document that was read. 0 of 1301 exhibits are hashed (0 from a Wayback Machine capture because the issuer blocked the fetch); 0 could not be fetched and are listed as such.

A hash of a web page changes whenever the page's markup changes, so a mismatch on an HTML source shows that the page changed, not that the document did. Hashes of PDFs are the stronger check. Copies of documents the project may not redistribute are kept private; copies of public-domain documents are published only where the exhibit page shows a local copy.