Google’s John Mueller said on webmaster hangout about the issue of treating some 404s as 301s. John Mueller speaks on this as Mihai Aperghis asked this thing to him.
Google doesn’t consider the to be URL as a 404 and the new URL is a spic and span URL. It just considers the to be URL as a sanctioned to the new URL. Utilizing a test live URL it shows a 404 yet doing the ordinary URL investigation it just shows the Google site the accepted is presently the new URL rather than 404.
The new url, which was a complete duplicate of the old url that was 404'd, is now ranking exactly where the old url ranked for queries. So Google is treating the 404 like it was canonicalized to the new url (even though it 404s). Again, fascinating. 🙂 cc @mihaiaperghis https://t.co/Pa1FgA3lgO
— Glenn Gabe (@glenngabe) December 17, 2019