What's the difference between Previous 12 Months and Last 12 Months?
I assume that if we look at today, The Last 12 Months would be July 2010 - June 2011 and the Previous 12 Months would be July 2009 - June 2010? Is that correct?
In that case you could use the Addmonths() function and add a negative 12 (-12) or 24 (-24) as number of months. Try searching for "addmonths" in the forum to find some examples on usage.