[Formendacil]

One thing that should not be forgot is that 3000 years passed between Isildur's day and Boromir's. Trying to find Rivendell on the basis of information that old would be like trying to find Babylon on the basis of a text from Homer's day. Not impossible, perhaps, but definitely difficult.

Of course, Gondor had a continuous history throughout that time--but even if you look at ancient Egypt, going from the foundation of the Old Kingdom, c.-3100 B.C., to the time of Cleopatra, c.-50 B.C., I doubt there was all that much information from the dawn of ancient Egypt that was likely still in circulation under the Ptolemies.

Mind you--I'm overlooking the fact that Egypt started out primitive (technologically and communicatively) and advanced as it headed towards the Annis Domini, whereas Gondor started out in all its Númenorean splendour--but I think it's still fair to say that such information could certainly be lost over time--and Boromir seems to have been sent off rather rapidly. I doubt a full search of Gondor's archives, such as Gandalf made to find Isildur's note, would have had time to be made.