[Eagles Talon IV]

Are the planets or other asteroids this particular one will pass by not known already? It seems if this asteroid can be identified 29 years out, so then can the celestial bodies it will come near. It's just mathematics and it seems as if someone has done their homework if the probability of a collision is at .018%

I don't know this for a fact but it is probable that ones chance of being struck by lightening is greater then that.

[RightWhale]

They can project the path 20 years out to be within a disc of a certain diameter with a sigma of some value. They may be 99% sure the asteroid will pass through a disc 48,000 miles diameter, but where within the disc they cannot know. The actual path will be determined by deflection by the gravity of the various planets in the meantime, and the amount of deflection will vary depending how near the asteroid passes in turn to each planet.
The uncertainty increases with each pass near a planet.