Throughout the Dragonsong War, their astrologians claimed to track the movement of Nidhogg's forces by watching the Dragonstar. A star that we now know is mostly a polluted wasteland due to the war with the Omicrons, and that Midgardsormr had fled from before he settled on Hydaelyn/Etheirys.

So why would watching a dead star allow Ishgard's astrologers to know movement of the Dravanian Horde? Or were Forlemort and others just talking out of their ass the entire time about "tracking the horde's movements"?