Can anyone suggest a way of doing this ...

I have a file detailing the results of 10 Area Managers. Each AM has a
Sheet - column A lists weekdays throughout the year and C - J represent 8
product groups. On a daily basis the results for each AM are entered on
his/her Sheet.

I need a summary sheet that will show the results between any given periods
during the year. I can only think of doing this using SUMPRODUCT (and =,
<= parameters) but that would seem to mean having to create 80 (ie; 10 x 8)
named ranges.

Is there a simpler way?

Many thanks.