If not, kudos to you for tackling the object model with reckless abandon.
Sometimes that is the most exciting way to learn, but for those less adventurous I will briefly cover the topic here.
For documents, Before and After properties are guaranteed for post events, such as Item Updating and Item Updated, but Before properties are not available for post events on list items.
For example, if you define an instance level variable in the class to store data in the Item Updating event, then try to access that data in the Item Updated event, you will find that the data is not there when you go to check it in the Item Updated event.
New value means that the correct value for the column was available.
Changed value means that the correct updated value was available.
The first time the Item Updating and Item Updated events fire it is in response to the document properties changing.
The second time they fire it is in response to the document being checked in.