Duplication has been a hot topic now since the first Penguin update. Since then, most organisations are wary of duplication but in recent years, duplication has become an integral part of some aspects of content development
This happens in large multi-national websites, particularly where they have multiple markets with the same language. This is a well known issue and I deal with it in “Is HREFLANG useful“. We use rel=”alternate” and specify the market for each version of each page in each market. Google then recognizes that each page is relevant to each market and it indexes all pages. Without the HREFLANG tag it will index the first version it cmes across and may ignore all other versions.
For sites which are not responsive, a lot of companies create a separate version of the site for mobile. This is accepted practice but you need to tell Google that they are different versions of the same page. Google has an excellent article on how this works and how to implement it. This is similar to HREFLANG also in that it can be applied via sitemaps but it also requires a canonical link from the mobile version to the desktop version.
Building an AMP page, to exploit Google’s new AMP protocol means adding an alternative version of the page, with a specific technical structure. In order to build a valid AMP page you use cut-down libraries of HTML, CSS and some JS, also AMP pages must have a couple of things in place
- Schema must be applied (use JSON-LD embedded in the page)
- AMP pages must use canonical to point at the regular page version
- Use rel=”amphtml” on the desktop page to point at the mobile version
Having valid AMP pages automatically avoids duplication issues, but poorly implemented AMP could cause dupes.