I have been known to use Hypothes.is to annotate 404 pages with a signpost to the correct place, especially if getting to the correct one isn't as easy as putting the original URL into the Wayback Machine. I always tag them with the "uncool URI" tag. (Funnily enough, some of the pages I've had to use this tag include ones on w3.org or ones associated with projects like runmycode.org or operated by folks at the Internet Archive.)