if "gain" is raw aas, there is an xp bonus to aas at different levels of completion; I wouldn't expect them to all be the same unless you all started at the same base #.
In fact, you'll notice that the character who started with the least aas, earned the most over the time period, and each followed this pattern, except for Buka, with an xp penalty.
edit: I realized I didn't explain super clearly: each character may have received the same total xp points, say, 500,000. However the xp required for aas 1-50 is different than that for 200-250. The character who starts with 0 aas might make 20 out of 500k xp, while the character with 200 aa only makes 12.
The numbers and ratios in this example are completely made up and are only to illustrate this concept.