[seanwilson]

The guide from https://www.checkbot.io/guide/seo/ is focused on technical/on-page SEO but Google makes some mentions of how it treats duplicate content across the web here:

https://support.google.com/webmasters/answer/66359?hl=en

> Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Mostly, this is not deceptive in origin. ...

> Google tries hard to index and show pages with distinct information. This filtering means, for instance, that if your site has a "regular" and "printer" version of each article, and neither of these is blocked with a noindex meta tag, we'll choose one of them to list.

> In the rare cases in which Google perceives that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved.