One of the design aims of the IBAN was to enable as much validation as possible to be done at the point of data entry. In particular cases where 00 is a valid check digit, 97 will not be a valid check digit, likewise if 01 is a valid check digit, 98 will not be a valid check digit, similarly with 02 and 99.
Clearing requirements
All bank offices participating in any of the following clearings must have a sorting code:
Every bank office with a sorting code does not necessarily participate in all these clearings, however, once a sorting code has been issued to a bank office, the same sorting code will be used in all of the clearings. Every company that does financial transactions can benefit from having a SORT Codes database to verify it's payments, minimizing the risk of mistyped or incorrect data.