Create a calculated field with following formula & replace this with your date field.
if datepart('year',[Order Date]) < 2013 then 'Total 2012' else
str(datename('month',[Order Date]))+' '+str(datepart('year',[Order Date])) end
I have not tested it yet but hope this may work for you.
Thanks. I didn't think to do it as a string field, but I think that will work.