Thanks Juraj, that set me on the right direction. I'm trying to expand on this a little.
The data I have expands to over 10 years worth of values. Using the same table as before, I'm now working the set analysis so that the calculations are generated as per the selection i.e. if I select 2012-Q3, I should get all values between 2012-Q3 and 2011-Q4 for the 1 year aggregation
I'm using a variable to generate the max row number (vMaxQtrSeq), so in line with the above table my expression is something like this: