I'm new to banking and I know this may be a stupid question but I 'd like to ask for clarification on this.

John has a personal checking account with the bank. John later opens a new business account for ABC, Inc. Then is ABC Inc. considered as a "New Customer" or an "Existing customer" just because the authorized signer already has an existing personal checking account with the bank? If John opens multiple business accounts later for multiple different businesses later, should each business be considered as a "New Customer"?

Thank you for your help.

ABC Inc. is a separate entity from John and must be treated as a new customer.

Here we tell the CSRs if the person or entity has to be "created" to add to our system, they are a new customer.
I should add, if they are in the system with no open accounts, they are a new customer as well.

The corporation is separate from its ownership. It's a new account. If the same ownership later opens additional accounts for other corporations or LLCs, each corporation or LLC would be a new customer.