AWS has long had AZs that were not exposed via EC2, as somebody else pointed out, the S3 FAQ gives the game away that some regions have a 'hidden' AZ.

They are slowly adding a 3rd AZ to regions that didn't have one already.

E.g.

https://aws.amazon.com/blogs/aws/now-open-third-aws-availabi... https://aws.amazon.com/about-aws/whats-new/2018/03/aws-govcl... http://www.datacenterdynamics.com/content-tracks/colo-cloud/...