Convert the dates in one column so that you have Year, Month, and Day as real dates. Do this for every worksheet. Then use the Pivot Table wizard, Choose Multiple Consolidation Ranges to compile your data into one Pivot Table.

Having done that you can now group by year, month or day or even number of days to produce various reports.

Another approach would be to combine all your worksheets into one worksheet and convert your dates to real dates then create a Pivot Table and group by date the Years, Months and Days as required.