Spoiler Alert! It is unlikely that Voldemort ever read of heard of "Tales of Beetle and Bard" as he grew up in a Muggle orphanage, and if he did later he probably just saw it as a tales for children. He would not think to look more into it. As Dumbledore says to Harry in The Half Blood Prince: "Of house-elves and children’s tales, of love, loyalty, and innocence, Voldemort knows and understands nothing. Nothing. That they all have a power beyond his own, a power beyond the reach of any magic, is a truth he has never grasped." He did not know that the ring and the wand were Hallows, merely objects; a family heirloom from a powerful pure blood family and a exceptionally powerful wand. I doubt that he knew about the existence of the cloak.