out of interest, I would have gone the route of a sumproduct table that calculated all "scores" above a certain date MINUS all scores above your second date.....

=sumproduct((a1:a1000>date1)*(b1:b1000)) - sumproduct((a1:a1000>date2)*(b1:b1000))

I find it easiest to put the 2 dates in specific cells and refer to those cells in the formula (where for ease and clarity I put date1 and date2)