Development deals run through special purpose vehicles, trusts, and joint ventures, so a wrong digit in an ABN is a real problem. It's checked the moment it's typed, on every entity, not just at signup.
ABN runs the actual ATO modulus-89 checksum, and ACN runs ASIC's weighted check-digit formula. Both are flagged immediately if they don't add up, on creation and on every later edit. BSB and account number are checked too, at 6 digits and 4 to 10 digits respectively, catching a mistyped digit count on the spot.
Entity validation