Dynamically Variable Ranges

In my worksheet cell A1 represents a financial reporting period from 1 to 12. It also represents the number of columns I need to sum in order to arrive at the desired period totals in this income statement worksheet. How can I get Excel to automatically change my SUMPRODUCT function as the value in cell A1 is changed from 1 to 12?

Here is a sample cell formula:

=SUMPRODUCT(ISNUMBER(MATCH(GL1SHL.XLS!$A$2:$A$332, {"4620","5220"},0))*(GL1SHL.XLS!$CE$2:$CE$332)*(GL1SHL.XLS!$I$2:$T$332))

The above formula represents the totals for period 12 for General Ledger accounts 4620 and 5220.

GL1SHL.XLS! references the workbook that has the financial data exported from my G/L application.

$A$2:$A$332 is the column which contains the G/L account number to be matched.

$CE$2:$CE$332 references a cell that resolves to the value 1 or -1 so that expenses which are exported as positive values become negative.

$I$2:$T$332 represents the 12 columns and 332 rows that contain all the financial data necessary to calculate the income for period 12 with each row representing a different G/L account's 12 periods of financial data. I need a method to dynamically replace the 'T' in $I$2:$T$332 and resolve it based on the value in cell A1. So if A1=1 then 'T' becomes 'I' and if A1=2 then 'T' becomes 'J' etc.

I would like to do this as a macro substitution instead of having to make 12 worksheets, one for each period, or instead of having 12 nested loops.