This issue is only with Google search. I don't see the issue in Bing.

Anyway, as you can imagine, I do not have time to look at every search engine (duck, ask, baidu, etc) ; I only pay attention to the search engines that drive "real" traffic to the site.

If you are really interested in helping out, you can access to the search console and webmaster tools for each of those search engines; but honestly, you will need to spend considerable time doing each possible keyword combo to see exactly what Google is doing. I only stumbled on this working on "soft 404 errors", which I now understand are not "real errors" but "Google's optimization". "soft 404 is very misleading.

Anyway, Victor, I only report what I see and what is happening at unix.com and why our index is getting hammered by Google with the "soft 404 errors" reported in Google Search Console, where Google has rejected the links and deleted them from their index; and where i can test them.

Also, the complete algorithm of what and how Google is matching these "error" and "not found" words is not known to me (it is a closely guarded Google secret) and nor is it published by Google.

Anyway, it's wearisome to say the least.