There's a wealth of information available to you on TrueAchievements, and tapping in to all of it can be quite daunting.
tip. If you go into My Stats and choose Milestones you can see the exact dates you smashed through the key numbers in graph form (with pop-up dates as you hover over the plotted points), and as a complete list too.
Have a look. When was the last time you broke through a big TA score number?