Curtis, he did bear a remarkable resemblance to Number 6. That was lucky for both Curtis and Number 2, as there was no need for the use of plastic surgery. It is also fortunate for Curtis that Susan had died a year ago, which means that if he had no family, no-one would miss Curtis now that he's deceased, otherwise there might be some explaining to do, if not in The Village then elsewhere!
Whilst it is true that every government department guards its work obsessively, if Curtis was an absolute doppelganger for ZM73/Number 6, it is highly unlikely that no-one had ever remarked to him about his double. Even if ZM73 and Curtis had never seen each other.
Be seeing you