We use Experian's Knowledge-Based Authentication, which is similar to what ben1040 mentioned above. It is based on your name, address, and sometimes your SSN.
Experian's KBA is not adequate to prove identity for legal purposes in any state, or for federal purposes. My banks won't even use it to verify identity for credit purposes.
What incompetent lawyer told you that you could use it for the basis of your service? Moreover, what incompetent lawyer told you that you could offer such a state-specific thing as notarization services nationwide?
You can read more on Experian's KBA here: https://www.experian.com/products/pdf/knowledge_iq.pdf Or here: https://www.experian.com/esolutions/esolutions/products/frau...