How to track the scroll position of a WowScrollBoxList

[LudiusMaximus]

I would like my addon to keep track of the current scroll position of the achievements frame scroll box.
But the scroll box only seems to have an OnMouseWheel script.

AchievementFrameAchievements.ScrollBox:HookScript("OnMouseWheel", function(self)
  print(AchievementFrameAchievements.ScrollBox.scrollPercentage)
end)

The same goes for its scroll bar.

AchievementFrameAchievements.ScrollBar:HookScript("OnMouseWheel", function(self)
  print(AchievementFrameAchievements.ScrollBox.scrollPercentage)
end)

But what if the user changes the scroll position dragging the scroll bar or clicking the scroll bar steppers?
Are there scripts to hook as well?

Is there not an easier way? Like a scroll frames' OnVerticalScroll script?