Certificate Transparency Turns Certificate Issuance Into an Observable Event
A certificate can be valid in every cryptographic sense and still be a security incident for the organization named in it. The issuing certificate authority may have followed its validation process, the signature may verify, and browsers may accept the chain. If the certificate was requested through a compromised account, an unintended validation path, or an infrastructure mistake, none of those properties establish that the domain operator expected it to exist.