Why do Google Analytics reports display aggregated values in header that are not the sum of all rows?
Solution 1:
The sum does not match up, and it is intended, because what you get as total is the count of single users over the analysis period, while rows lists user count on the dimension basis (picking the dimension day for instance, one user, counted as one above, could have made a visit on day 1 for instance -therefore incrementing 1 on day 1 - and another visit on day 3 - also incrementing users count for day 3)