The rings were done aproximately in 1300 during the 2nd age. Sauron has been captured later on by the last king of Nùmenor, Ar-Pharazôn who bring him on his island. The bright Dark Lord made quite a mess on this mighty island that lead to the submersion and exodus of the Nùmenoreans. During a long time Sauron was the prisoner of the mightiest king ever the king who wants to rule the world. How can Pharazôn could've let Sauron keep the ring on him he knew Sauron had a «magic» ring that give him incredible power. More than anybody else he wanted those kind of power, he always been a LITTLE BIT evil. I don't think he would've let this chance go. If Sauron left the ring in M-E who could've hold it for him, or hide it from the elves? I'm really wondering about that. Is there any explanation some where I was hoping to find some in the Unfinished of the 2nd but there is nothing. Once again ther's a unfinished bridge over Tolkien's Middle-Earth Ages.