Well this isn't very helpful because display names are most useful as Last Name, First Name which no one wants to display in the address.   If one uses the 'first name middle name last name' blocks there's no place for a spouse.  So there's no way under the system you're describing to mail an invoice to a married  couple 'Joseph & Cynthia Walsh' because no one wants that customer listed under J in the customer list, and there's only room for one name in the blocks.