Hi,
Yes, you will not receive the SSN back in the response when you perform a query, but you can perform a search by SSN which will return the patient that matches that SSN. For SSN, and NHS, you'll need to use identifier parameter to create a patient with an SSN.
In our sandbox, the structure of a SSN you'd use would look similar to below:
When performing a search, you'd use the "identifier" search parameter with
http://hl7.org/fhir/sid/us-ssn as the system. Again, this is only within our sandbox and when you move to a client who has NHS numbers set up, the system and type for the identifier would change. You can read through the Patient Create documentation on
fhir.cerner.com for DSTU2[1] and R4[2] for more information as well.