If "Invoice type code" (BT-3) contains the code 384 (Corrected invoice), "PRECEDING INVOICE REFERENCE" (BG-3) should be provided at least once.
(/ubl-invoice:Invoice | /ubl-creditnote:CreditNote)[$supplierCountryIsDE and $customerCountryIsDE]((not(cbc:InvoiceTypeCode = 384 or cbc:CreditNoteTypeCode = 384) or (cac:BillingReference/cac:InvoiceDocumentReference)))