[anon1385]

How can I prove a negative?

I can only point to what the Google AMP documentation says, where they state that you have to allow your site to be served by Google AMP Cache to count as an AMP site: https://developers.google.com/amp/cache/faq and https://developers.google.com/search/docs/guides/about-amp

Maybe they don't follow their own docs and there are sites out there not cached in the Google AMP Cache that still get placed in the carousel. I have no way to prove that without being able to test every single possible search term (plus all the other variables like location which affect the results).

[ucaetano]

The wording is that you have to allow you page (not site) to be cached by any CDN.