Canonical Tag Can be on Either AMP Page or Legacy Page within an AMP HTML Pair
If you have the rel=amphtml tag set up correctly, Google can pick up the canonical tag from either page in the pairing.
HTML & AMP Pages Containing the Same Content Will Not Be Negatively Seen As Duplicate Content
Having the same content on both HTML and AMP pages is not negatively seen as duplicate content by Google. However, it can lead to competition between the pages within search results. To avoid this, John recommends concentrating the value of both pages using the relevant rel alternate link and canonical tag.
You Can Use Different Types of Structured Data on Alternate Versions of a Page
When implementing structured data, it’s fine to use JSON-LD on the desktop version of a site and to use microdata on the AMP version of a site, for example.
Same URL Can’t Be Used for Mobile & AMP if Serving Different HTML
You can’t use the same URL for both mobile and AMP if they’re both using different HTML as Google wouldn’t know what to show for mobile users. You can use the AMP as your main mobile page instead.
Geotargeting AMP is Possible But Difficult to Implement
Theoretically, you can geotarget AMP pages to countries with poor connection speeds. However, this wouldn’t be easy to implement, as Google tries to keep a global view by associating an AMP version with the normal version of the page.
Google Recrawls Indexed AMP Pages to Update Cache
If Google find an AMP page that has already been indexed, a recrawl of that page will be triggered after a period of time to update the AMP cache.
AMPs Which Canonicalise to Noindexed Pages Won’t be Valid
If a page is noindexed which is connected to an AMP equivalent, then the rel=amphtml link will be dropped too and the AMP won’t be valid. If the AMP is noindexed then it will be removed from the index and the traditional page will be kept.
AMP URL Configurations Are Equivalent to Google
You can have AMP on a subdomain, subdirectory or on a parameter, it makes no difference to Google. Your configuration depends on what makes the most sense for your website and tracking methods.
A PWA is a Bigger Investment than AMP as a Solution for Improving Mobile Usability