Amelia Bones learns something at time x is an event happening at time x and information of that event could be taken back to time x − 6. If the information that she gets is from time x + 4 then that information could only go back to time x-2.
But she got information from time x + 4: the fact that there was interesting information to get at that time.
Think of all of the logic puzzles where you have (just) enough information to deduce that somebody else had enough information to deduce that somebody else … etc.
Amelia Bones learns something at time x is an event happening at time x and information of that event could be taken back to time x − 6. If the information that she gets is from time x + 4 then that information could only go back to time x-2.
But she got information from time x + 4: the fact that there was interesting information to get at that time.
Think of all of the logic puzzles where you have (just) enough information to deduce that somebody else had enough information to deduce that somebody else … etc.