According to Google, beginning in February 2018, Accelerated Mobile Pages (AMP) and canonical pages have to match or have very “close parity.” Any AMP pages that don’t match the content of canonical pages “will not be considered for Search features that require AMP, such as the Top Stories carousel with AMP.”
For some time now, content parity has been a requirement, and now Google is stepping up enforcement. At the same time, the company is also emphasizing that AMP isn’t a ranking signal and it will not incur a penalty, other than the above potential visibility, for pages that fail to comply.
The reason why Google is doing this is because it’s seeing AMP used, in some limited contexts, on “teaser pages” that offer only limited content. An example that Google uses is a news article whose AMP page features a simple excerpt with a prompt to click for the “full story.” In these situations, users are being required to “click twice to get the real content.”
If a non-compliant AMP page is found after the deadline, Google will send users to the “non-AMP equivalent.” If that equivalent page is slow loading, users will, more than likely, abandon it. Google also says that it will “notify the webmaster via Search console as a manual action message and give the publisher the opportunity to fix the issue before its AMP page can be served again.”
Google’s reason behind this is to promote a better user experience. It also wants to protect the integrity of the AMP initiative itself.
Source – Greg Sterling