Hi there,this is most likely because you have visitors who feature in
both time periods. E.g. Someone has visited on Dec 1, and then again on
Jan 1. They will be counted in each date range. So therefore you cannot
simply add two date ranges for unique visitors to get the total. Your
first report, from Sep 3 to Jan 31 will give you the total unique for
that time period.It almost never makes sense to add together unique
visitors.