Count entire workbook?

Is there a way to count a specific column through an entire workbook, including all worksheets? Each worksheet is numbers 'Week 1, Week 2 etc'.

My problem is I'm trying to count specific dates within these worksheets but sometimes week 2 will have dates from week 3 in it due to week 2 work not being done on time.

I'm thinking there isn't a way to do this, but just to be sure I thought I'd ask.