Retrieves a EXT_USER_DENY_SELF_REG row for a given customer group ID and user type code. The presence of a row indicates the user type/customer-group combination is on the block-list, enforcing BR-EU-02.
Note: Statements marked with * were inferred from code structure, naming conventions, or contextual evidence where direct confirmation was not available in source artifacts. Statements marked with ** could not be confirmed; treat as unknown until verified.