Search for fiscal quarter and year

The headings DO include the strings "1- ", "2 - " etc.

The attached spreadsheet lists the actual headings.
Note the formula in cell A2 is =SUM(J2:T2). what I'm trying to do is replace the hard-coded T2 with the cell reference of the quarter previous to the current quarter, shown in B1, taking the current year into consideration.

In this example, the earliest 'Past Due' quarter is Q4 2007, so that is the data in cell J1. However, if that customer pays their bill, the next earliest Past Due quarter will become Q1 2009, and everything will move left accordingly, so the rightmost cell reference will change. (Col J will always be the first column in the range).

Thanks.