Licensing confusion

Hi, there's conflicting documentation around Licensing.

I see on [this page](https://www.boost.org/doc/contributor-guide/requirements/license-requirements.html) that it is implied that code included in Boost must meet the licensing requirements mentioned there but is not required to use The Boost Software License.

On [this other page](https://www.boost.org/doc/user-guide/faq.html#_licensing) it says:
> The Boost libraries are licensed under the Boost Software License

So which is it? Are boost libraries licensed under any license that meets the requirements or are they under The Boost Software License?

The reason I am asking this question is because I've found that [boost.serialization](https://github.com/boostorg/serialization) does not include a license for every file so I am looking to confirm the overall entire boost license covers the code from this library