The Internet Archive ("Wayback Machine") provides only fragmentary coverage of the web. Search for any particular content from past years and that will quickly be apparent. There's plenty of detail
here about how and why the Archive is not complete.
Nor is the Internet Archive itself in any way assured to be permanent. It's not "the internet" - it's a data-archiving initiative by a particular private organization that may or may not last.
Nothing on the web is permanent "by definition". On the contrary: by default, web content is highly fugitive.
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