O Um Anel deu a Sauron o controle dos Nove, mas quando foi tirado dele ele ainda possuía o poder de controlá-los (ou, pelo menos, ele o recuperou no final da terceira idade). Por que é isso? O artigo da Wikipedia menciona que ele desenhou os Nove para ele, mas não como.
Depois que os usuários dos Nove Anéis se tornaram os Espectros do Anel, Sauron - que na época ainda possuía o Um Anel - levou seus Anéis deles. Em uma carta, o professor Tolkien escreveu,
Sauron ... still through their nine rings (which he held) had primary control of their wills.
de As Cartas de J. R. R. Tolkien ; ênfase minha.
A carta 246 explica que, mesmo que outra pessoa tivesse controle sobre o Um Anel, os Nazgûl ainda obedeceriam a Sauron:
Sauron sent at once the Ringwraiths. They were naturally fully instructed, and in no way deceived as to the real lordship of the Ring...But the situation was now different to that under Weathertop, where Frodo acted merely in fear and wished only to use (in vain) the Ring's subsidiary power of conferring invisibility. He had grown since then. Would they have been immune from its power if he claimed it as an instrument of command and domination? Not wholly. I do not think they could have attacked him with violence, nor laid hold upon him or taken him captive; they would have obeyed or feigned to obey any minor command of his that did not interfere with their errand - laid upon them by Sauron, who still through their nine rings (which he held) had primary control of their wills..
246 De uma carta para a Sra. Eileen Elgar (rascunhos) Setembro de 1963
De contos inacabados "Caça ao Anel":
At length Sauron resolved that no others would serve him in this case but his mightiest servants, the Ringwraiths, who had no will but his own, being each utterly subservient to the ring that had enslaved him, which Sauron held.