How to confirm endpoints are FIPS enabled in US GovCloud

Hi all

I am working to ensure our environment strictly uses FIPS VPC endpoints within AWS GovCloud.

While reviewing the FIPS Endpoints by Service documentation - https://aws.amazon.com/compliance/fips/#FIPS_Endpoints_by_Service, I noticed the list appears incomplete. For example, ssmmessages and ssmmessages-fips are not explicitly listed, yet openssl testing confirms it supports TLS v1.3 and AES ciphers:

openssl s_client -connect ssmmessages.us-gov-east-1.amazonaws.com:443
openssl s_client -connect ssmmessages-fips.us-gov-east-1.amazonaws.com:443

The openssl results said the endpoints negotiate FIPS-approved TLS ciphers - https://repost.aws/questions/QUoQCzOCo2TIaciweOenk-1Q/govcloud-fips-endpoint-email-smtp-fips-secretsmanager-fips-us-gov-east-1-are-available. But can it guarantee that those endpoints are fips enabled?

Does anyone know of a failsafe way to confirm 100% that an endpoint is FIPS-validated? I want to ensure we aren't relying on "incidental" compliance that hasn't been officially audited.

Thanks.