The element <externalPubIssueDate> contains date information about the referenced publication.If the <externalPubIssueDate> contains a date in textual form, then that text will be displayed to the user. If only the attributes are provided, then it must be displayed in the ISO 8601 calendar date format YYYY-MM or YYYY-MM-DD. If the attribute month of <externalPubIssueDate> is populated then the attribute year must also be populated. If the attribute day is populated then the attribute month must also be populated. Refer to default BREX rule BREX-S1-00061.