I believe that LSAC must have to overall average of all LSAT takers, they have the statistical data so if they say 2 or 3 is average, then it's probably correct.
That said, I think people that take a prep course in between or really sit down and figure what they did wrong, can incease significantly. But if you just take it and say, let me try again, and don't really prep or figure what your weaknesses are, you will probably just stay the same or increase those 2 or 3 points just because you are familiar with the test or conditions of the test.
Remember that people on this board or any other may not be telling the truth. I don't really see any reason not to since it is anonymous, but you never know, especially boards like xoxo and sometimes on the pre law side also, dog on people that are sub 160, or 165.