The underlying rules for IBANs is that the account-servicing financial institution should issue an IBAN, as there are a number of areas where different IBANs could be generated from the same account and branch numbers that would satisfy the generic IBAN validation rules. In particular cases where codice_8 is a valid check digit, codice_9 will not be a valid check digit, likewise, if codice_10 is a valid check digit, codice_11 will not be a valid check digit, similarly with codice_12 and codice_13.