As with many other Internet "platforms", Internet Archive (IA) content is often uploaded by individuals. Just as with YouTube and other platforms, IA responds to requests for takedown if a copyright holder complains that the content violates copyright ownership. However, those who upload material come from many different countries and their laws often vary from U.S. law. So, as with other platforms like YouTube, the content is assumed acceptable unless a copyright owner requests takedown.
Just as with YouTube, a lot of older recordings, especially from broadcast or LP or old CDs are either out of copyright of ignored by the copyright holder because no longer available for sale commercially.
Book publishers have been more aggressive, engaging with IA in legal battles for years, so far unsuccessfully, regarding the IA book lending policy, which conforms to the same policies used by all public and university libraries nationally.
The IA copyright policy can be found at the bottom of this page.
https://archive.org/about/terms.php[/u]]https://archive.org/about/terms.phpJust as with YouTube, I think users can safely assume that, if the video/audio/or other material is there, no copyright holder has requested a takedown, and so can be downloaded.
Finally, under U.S. copyright law, if any material is made available for educational purposes and is not redistributed for commercial purposes, it can be legally shared with others (within limits). IA presents itself as a platform for historical and educational information.
In the end, I ain't fretting over this issue.