Also, the activity on the problem is not what determines if an AnswerValue is blank.  As mentioned above, if there is no activity on the problem after early March 2014, the problem won't even appear in this report.   So there must be some kind of activity on the problem after early March 2014.  However, if it is a checkbox or multiple choice problem and a particular *choice* has not been chosen since early March 2014 (but has been someone's final choice since October 2013), then the entry in the report _for that choice_ will have the AnswerValue blank.