Limiting x-axis values on a chart moving totals involved

[mayfs]

Hi everyone. First post. I'm collating rolling values for 12 periods and have two years worth of data. The first 12 periods are accurate but from period 13 backwards the data is not correct. Whilst all my data is included the chart function is working accurately for the first twelve periods. If I apply a filter then the moving totals are not correct. I've tried creating a flag that is my display period, but it still seems to impact the moving totals, with the graph going to rubbish.

As a work around is there anyway I can get the 'dynamically' changing moving-totals to become 'static' for the purposes of the report and display in the graph?

I'm open to any suggestions, be they x-axis filter or data manipulation. I'm suing 10.2.2 report studio.

Many thanks
Scott