[Rhod the Red]

"I assume had he broken the 'rules' then there would have been some sort of intervention from the Valar, thus his ring did not bring about any upheaval. Though still sufficient to warrant Gandalf's attention.

I would value your views and comments."

I think he made it after moving into Orthnac. The lore of the Rings of Power would only have been written, etc, in Middle-earth. About the time of The Hobbit, perhaps using the powers of that Ring to drive Sauron out of Dol Guldor. We know his 'devices' as Elrond called them, were used to drive him out.

You'd need to be pretty powerful to drive out a Dark Lord, even when reduced to some sort of spirit, out of a mountain. Even though Sauron pretended to be forced out. I'm sure he put up a fight of some kind, pretending to resist.

Yes, I think the fact he made it violated the mission of the Istari. We can only assume that by the time Sauron was driven out of Dol Guldor, and then started searching for the One Ring in the Anduin, then Saruman had violated the mission by doing likewise with 'spies'.