One of the reasons that the Heaven Sword and the Dragon Sabre were given such legendary status by wulin during HEAVEN SWORD AND DRAGON SABRE was that most of wulin did not know the two weapons' true origins, nor did they know their true value. They only knew of a legend that whoever possessed the Dragon Sabre would rule the world, and the only one who could challenge the sabre's owner would be the owner of the Heaven Sword. The assumption must have been that the weapons were very, very old...predating the lifetime of anyone then living.
Cheung 3 Fung, however, was old enough to remember a time when the Heaven Sword and Dragon Sabre did not exist. He was already 26 years old by the time Gwok Jing and Wong Yung created the weapons, and it must have taken some years before the weapons' legend began to spread around wulin (when Cheung 3 Fung was middle aged, most likely). That being the case, couldn't Cheung 3 Fung have dismissed all those legends about the Heaven Sword and the Dragon Sabre?