Both seem to be creations of the age before the age of legends. But it would seems like they would be something that are consistant every turning. Seems like the Horn would be used for every Age of Prophecy considering how Hawkwing talks to Rand. Do you think the Horn or something similar is created every turning or it's just forgetten and found again?

 

Portal Stones we know even less about. Who made them and how old are they? Are they constant major event in each turning?

It seems that the Wheel spins out whatever is needed to maintain balance. Perhaps these are present in some turnings of the Wheel, but in other turnings they don't exist.

In one turning there was a Triangle of Valere