Does adding a noindex tag reduce duplicate content?

[ChrisJFoster]

I've been working under the assumption for some time that if I have two (or more) pages which are very similar that I can add a noindex tag to the pages I don't need and that will reduce duplicate content.

As far as I know this removes the pages with the tag from Google's index and stops any potential issues with duplicate content. It's the second part of that assumption that i'm now questioning.

Despite pages having the noindex tag they continue to appear in Google Search console as duplicate content, soft 404 etc. That is, new pages are appearing regularly that I know to have the noindex tag.

My thoughts on this so far are that Google can still crawl these pages (although won't index them) so shows them in GSC due to a crude issue flagging process.

I mainly want to know:

a) Is the actual Google algorithm sophisticated enough to ignore these pages even through GSC doesn't.

b) How do I explain this to a client.

[TimHolmes]

Although adding a no-index will no doubt remove the page from the index, my suggestion would be to implement a canonical tag which you can use to point to the original/best source page. This way any links from the page will still be used for internal site crawling etc.

This way you are actually telling google that you have similar pages but one is the best that you want for indexation purposes.

rel="canonical" href="/original-or-page-you-want-to-rank-and-be-the-source.html" />