You are not supposed to lose abstergo score but if you don't play for a while, you may lose a few points.
Quitting a game has nothing to do with losing points.
You can only lose points the other way by losing matches and you can gain points by winning matches.
And you state in your link that you mostly only get 10 points per win. This is wrong. The higher the "domination" of the win, the more points you get.
For example, if you dominate all points in a domination match and win straight away in 2 minutes from the start (Doesn't exactly take 2 minutes to win, this is just an example), it gives you a massive boost of about 50-90 score.
However, if you lose a match and you get "dominated", you lose a lot of score. For me, the most I have lost in a match is 150 points.