Hello Aaron Burdick,
One thought for a solution would be to use calculated fields to bucket the data:
This would be a row level if/then statement to consider to get group A measure value:
if [DateField}>=1/1/2011 and [DateField]<=12/31/2013 then [measure] End
and so one through each grouping. The issue comes into how these measures are used in a view. If the values are just totals with the view not partitioning the view in any way this will be quite easy. See the attached example workbook with 2011, 2012 and 2013 sales and a percentage of 2011 sales divided by 2012.
I hope this helps.