While Plaid matches on multiple PII attributes for a user, SSN or ID number often takes priority in the Identity Verification data source matching logic. This means that we will check for records matching the SSN first, then check if the name, address, etc. provided match records tied to this SSN. This means an incorrect SSN can sometimes result in us pulling a different identity record altogether. When this occurs, the user will likely get no matches for the rest of their PII because it is being compared to the data tied to the (incorrect) SSN they entered.
In this scenario, the user will likely fail the Data Source verification check. If your template uses "Fallback to Document Verification", the user can still pass verification if their document is legitimate and their name and date of birth on their document matches what was entered in Data Source verification.