Torino Impact Scale
http://128.102.32.13/impact/torino.cfm
"Can the Torino Scale value for an object change?
"Yes! It is important to note that the Torino Scale value for any object initially categorized as 1 or greater _will_ change with time. The change will result from improved measurements of the object's orbit showing, most likely in all cases, that the object will indeed miss the Earth. Thus, the most likely outcome for a newly discovered object is that it will ultimately be re-assigned to category 0."
http://128.102.32.13/impact/downloads/categories.txt
I always thought Torinos were highly over-rated.....