Combining pivot tables

Hi all,

First of all, massive thanks in advance for anyone taking time to help me.

Every month I get a .csv file with tons of data. There are hundreds of 'Items' and each Item has 93 columns for data attached to it, examples below:

Item: A, B, C, ...
Region: Europe, North America, Africa, ...
Country: UK, US, Eygpt
Value: 1, 2, 4

What I want to do is combine the value fields for previous months (which are on previous pivot tables) in the current month's pivot table.

More detail:
The items are unique (and can be reduced or added to each month) and the other columns are static throughout the months; apart from the Value which changes each month. Each month I create a pivot table so that the data users can filter by whatever column(s) they wish. Now they want to see not just the monthly values but the combined quarterly and year to date numbers. This means getting the value field for previous months into the current pivot table so I can add them up with a calculated field.
Some of the difficulty here comes from the the fact that the items are every changing, so I can't just do a lookup of current items to get past data as i'll miss a lot of the items that have dropped out in the previous months.