tolkiens legendarium - Why did Sauron not have control of the three rings before the Great War?

Elrond said during the council that if Sauron gets the One Ring back, he will have full control of those who have the three rings. But why did Sauron not already have control of them before the Great War?

Answer

Because the Elves who possessed them took them off

From The Silmarillion:

But the Elves were not so lightly to be caught. As soon as Sauron set the One Ring upon his finger they were aware of him; and they knew him, and perceived that he would be master of them, and of all that they wrought. Then in anger and fear they took off their rings.

^{The Silmarillion V Of the Rings of Power and the Third Age}

Since they weren't actually wearing their rings anymore, Sauron had no ability to control them. Once he lost the One, his ability to command any of the Rings of Power was lost¹; in fact, there's evidence to suggest that he was only able to control the Nazgûl because he had the Nine in his physical possession.

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¹ Hence why the Elves considered it safe to put them back on and start using them