Need help with Moving Annual Total formula by Product, State, and Zip

I am trying to enter a formula that will calculate a rolling 12 month annual total in column N of the attached spreadsheet. I need to work backwards to calculate the MAT beginning with the most current date in the spreadsheet rather than the oldest date. So I want to start with 2013-07 though 2012-08 and then calculate 2013-06 through 2012-05 and so on.Moving Annual Total spreadsheet.xlsxMoving Annual Total spreadsheet.xlsx The attached sample spreadsheet contains Products in column H, Sales in Column G, the 3 digit zip code in column J, and the month in Column L. For example, I need to figure out the 12 month rolling total for all Carnations in the state of NH within zip code "30" from 2013-05 through 2012-06. Then the next line should calculate the rolling 12 month total for Carnations in NH within zip code "30" from 2013-04 though 2012-05 and so on for each line in the spreadsheet.

Please see that attached. I've used a user defined formula (ALT F11 - Module 1 to see the code). It's a bit slow to calculate but gets there in the end.

Note that this is now a macro enabled workbook.

Thank you very much. That worked great! I really appreciate your quick response and solution.