The way the regulation is structured, beneficial ownership data is supposed to be at the legal entity customer level. The opening of a new account is a triggering event to either gather that information for the first time or to update the information. The only reason accounts beyond that time is due to retention requirements, but so long as you maintain the BO data (and all of it's iterations at the entity level) for five years from the date that the last remaining account is closed, you'll be able to comply.
So, in your example, what ideally should have happened is that you had the authorized representative (after verifying their authority) confirm that the current BO data was accurate; or, provide you with the new data which would "overwrite" the last version.
If that person needed to be able to conduct transactions on the account, but the ownership didn't change, then you should just add them as an authorized signer.
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CFE, CAMS