"Illegal?" Probably not in the sense you intend. It's an error. A violation of proper procedure. It's addressable and correctable through a very cumbersome and likely expensive process that, likely, requires an exhaustion of administrative remedies through the department of vital statistics. Whatever costs are incurred in seeking revision to the DC, including costs associated with the pursuit of court action after a denial of administrative remedies, are not recoverable. And no action to correct the DC can be initiated until a probate proceeding has been initiated to establish the legal authority of the person requesting revision to act on behalf of the decedent's estate.