Why can the customer repeat the same code and the same commercial ID?
Because not all users employ those fields for the same things. For example, you might use the
Code field to designate residential versus commercial customers, or delivery route number, or tax exempt status. And different branches of a customer might have different points of contact, telephone numbers, and billing addresses, yet operate under the same business identification. So you would want to create them as different customers but duplicate the business identification.
Why does the program not support a custom field Customer Code to be a unique number
I support the idea of having a way to track duplicate accounts (using reference numbers) in the customer, employee, supplier, fixed asset, intangible asset and documents (Payment, Receipts etc),
For now, you can capture your customers on a spreadsheet (with prenumbered rows) or database (Access) first and batch update Manager to ensure each customer has a unique ID.