Your responses appear to be trending negative and mine won't reverse that flow. The emphasis on identifying the "primary" owner is misplaced. Legally that term has no meaning whatsoever. Operationally, it simply means the first person listed in the account title. If the account title is "Ken or John" your CIP should place exactly the same amount of emphasis on obtaining and verifying the critical information on both customers.
You must obtain the four pieces of identifying information on all customers prior to opening the account. You must verify the customer's identify using documentary or nondocumentary methods or a combination thereof within a reasonable time after opening the account. (As John suggests, only common sense, not the law, would require you to apply that same analysis to a "mere signatory.")
Any lesser process could and should be treated as a violation of law.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.