There is a known issue of some sorts with following the Google help documents around getting Google to pick up on your noindex tags faster through the fetch as Google. John Mueller of Google is aware of the issue and said the workaround "is to test the page live without noindex, then add the noindex before you submit it for indexing."
Here is the issue described by Angie Biron Ren who posted this on Twitter:
Added noindex meta tag to some pages and @google's support guide says to request a *crawl* by using Fetch as Google, which is now the URL inspector, on the live page. But the only option is to request indexing. Could pose any problems? @searchliaison @googlewmc @JohnMu @methode? pic.twitter.com/SCMpfBcvog
— Angie Biron Ren (@src_angie) November 20, 2019
John confirmed it and wrote that workaround in response, here is his tweet:
Yes, that's a bit confusing. I noticed that with a test page recently too. I'll pass that on to the team. A workaround / hack I noticed is to test the page live without noindex, then add the noindex before you submit it for indexing.
— 🍌 John 🍌 (@JohnMu) November 20, 2019
Forum discussion at Twitter.
