You are correct a single physical entity can interact with A business in different ways resulting in multiple roles in Manager. For Manager to report on these external entries reliably they need to be linked within Manager. A single contacts database would be to cleanest solution in my opinion. Many threads / users have requested similar functionality. See Copy Customer to Supplier and vice versa - #2 by Patch
Or do you need to link customer/supplier with multiple divisions which you have entered in Manager as multiple customers/suppliers. If so a contacts database would need more structure.