When you are looking at a reader's profile from the administrative side, you will see both a log in the lefthand navigation panel and a challenge-specific reading log under the title of any current challenges.
The log allows you to see all reading logged over time for that reader. It will include reading that both pre-dates and post-dates your challenges. This is the log for all time for that reader.
The challenge log only takes into account the reading, activities, and/or points that will count toward that specific challenge.
It is always wise to check the challenge log if a participant feels they should have enough reading, activities, etc., to have earned a badge or prize but have not yet earned it.