Clueless Sauron?

Thanks. Very informative, and a very extensive discussion. So, if I've understood correctly, the argument was that Sauron did not initially know that the destruction of his Ring would mean the end of him, but when he finally found out that the Ring was still in existence it changed his views on the very feasibility of destroying the Ring. I still find it strange however that Sauron would not understand from the very start the nature of his Ring. Certainly, as you stated, he seemed to know exactly what lay in store for him when he spotted Frodo at the Sammath Naur.

Another question. It seems to me that Sauron did not learn about Isildur's fall by the Gladden fields until very late in the Third Age, otherwise he would have had the river searched much earlier (and found the Ring). It is stated at the Council of Elrond that the tale of Isildur's fall was known only to a few (in Arnor) and to nobody at all in Gondor. How did Sauron manage to hear of it? Did he perhaps finally hear the long forgotten story of a captain of an Orc host which had been passed down through the centuries?