dynamically store a rolling six years of data in a table and have meaningful column field names and descriptions that can change year-to-year?

[<elehti@xxxxxxxxxxxxxxxxxx>]

How can we redesign this application to dynamically store a rolling six
years of data in a table and have meaningful column field names and
descriptions that change year-to-year?

We have a custom IBM i table with 12 monthly columns for the year 2007,
12 fields for 2008, 12 for 2009, and 36 for 2010, 2011, and 2012.
Sales history is summed and put into the appropriate month buckets.  
The data is downloaded to a spreadsheet and imported to a Windows sales
forecasting application which puts Forecast data is put into future year
buckets.  
We upload Future year data to our IBM i Sales Forecast File F3460 (JD
Edwards World).

In January 2012 I will need to delete the 12 fields for 2007 and add 12
fields for 2013 and modify the RPG program accordingly.

What redesign would allow us to dynamically store a rolling six years of
data in a table and have meaningful column field names and descriptions
that change dynamically from year-to-year?  So that I would never need
to modify the RPG program nor the file?