He... does not at all. This is barely a ceremonial denomination meaning that they are a designated mirror of official US documentation. This has even less of an impact than their basic clasification as a library, it's unilaterally decided by just the one senator and is mostly PR. They could have stored the same documents without the designation, even.
This is all a search or wikipedia visit away. People really operate on the basis of seeing a headline, not even bothering to click through and just... making up what it means in their heads. We really need to get better at this, it's been decades of Internet and centuries of newspapers.