It's been a while since I looked at MT, so this might be wrong, but here's what I remeber about the experience system.
1) One AT is given out per game.
2) There's a max of two ATs per calendar year that a character can gain in any one skill, IIRC, and the task to improve is quite daunting without at least a lot of ATs.
3) Add to that the fact that you can only attempt to improve one skill at the beginning of each session, whether it succeeds or fails.
Kinda simple, yeah, but I must admit I found that skill progression limits itself fairly well in those regards. Most of it depends on how much time goes by in each session. Measuring advancement in terms of adventure sessions is probably a better analysis than by calendar year, because of the impact on game play. It's only when you compare the number of campaign sessions per in-game calendar year between campaigns do you begin to see major differences between characters from different gaming groups, in terms of skill advancement, but within an individual group itself, everyone should advance reasonably in tune with one another and within the context of their character's capacities.
If I've misremembered something, please let me know,
Flynn