Aldy, you are doing this in java, right? You may want to use a more precise math api than the default, because there has been issues with the default API in the past.
Also, I've always been told that players that leave a game have no way of really knowing in the db... I think it's pretty much a lost cause.
Something happened in a game recently that got my blood boiling that is related. High pot, high GR game that was moving towards a 3-way (I was the 4th guy and eliminated last). However, russia, who CD'ed near the end, had a unit in warsaw that was right on the draw line. Fortunately, the last 3 worked it out (because 1 was an SC away from a solo) so that russia was eliminated from the draw, but it brought up an issue I can see happening... someone sneaking in on a draw and getting a major GR boost for no work, whatsoever...