Up until today, I’d been redirecting 404 errors on my new site to an archive version of the old site. I’m confident enough at this point that all of my previous content (that I’m concerned with) is properly redirecting and search engines are all updated with the new permalink structure. So I turned that off.
This is a companion discussion topic for the original entry at https://brettterpstra.com/2013/04/07/fun-with-intelligent-404-pages