How did he know???

This is key or pivotal in the film.

-in other words,he could not "snow" this incident because of its preciseness.

-mby

You've hit the nail right on the head.

In the first scene that everyone seems to have forgotten about, 'Elvis' is seen with the train driver who is now a truck driver and he appears to have sorted out his head by allaying the guilt he had for colliding with the car and killing the girl. 'Elvis' then sought out jonathan schaech's character and did the same for him.

He obviously couldn't have known about the cop's childhood and at that point in the film the audience are puzzled. At the end it is clear that it's Elvis' spirit within Keitel that is helping everyone out. That is the whole point of the film. When he meets the hobo on the train at the end he is obviously going to sort out his life too. Whether this was because the hobo was on the train involved in the original accident or whether 'Elvis' is going to sort out the reason why he's a hobo in the first place isn't clear.

Yes but spirits do not age. Elvis in order to be an older man as a ghost or spirit of himself would have once had to have been an older man in his lifetime but he never was an old man in 1977 or earlier. Therefore no spirit "footprint" would have been made. There would never in a million years be a spirit of a senior aged Elvis walking around. Can you see the ghost of your dead child as an old man when he never even lived to adulthood?