The origins of the format lay in the establishment of the Databank Systems Limited, a company set up by a consortium of competing New Zealand banks, to provide computing resources (development and operational) for the consortium members.
[1] Bank codes are coordinated by Payments NZ who administer the Bulk Electronic Clearing System (BECS).
A current list of branches as their associated bank/branch numbers is available for download from the Payments NZ website.
[5] The table below shows the account number suffixes as introduced by Databank Systems Limited from 1969.
[1] [6] Some banks (such as BNZ) include three digits of the suffix in their presentation of the number to the end customer.