Get PDF Properties missing signature_details

Is signature_details a real propery that this endpoint returns about a PDF? In the docs here: https://developer.adobe.com/document-services/docs/apis/#tag/PDF-Properties/operation/pdfoperations.pdfproperties.jobstatus

...the response sample clearly shows this property, as an array of objects, representing digital signatures and their respective certificates.

But it's missing from the schema itself, and indeed it's not returned when I use this endpoint to examine a signed PDF. It's also not returned when using the Get PDF Properties action in Power Automate.

Is this a deprecated property that just hasn't been removed from the sample?

Is there any way to retrieve the signature data from a PDF using the API?