Dynamic Charts - help setting up with named ranges

Hi,

I am new to posting on here as I usually find the answers I need by searching. However I'm coming up blank this time so I'm hoping someone can help me out.

I have data which I'm trying to chart. The numbers of rows in my data changes from month to month but the columns remain fixed. I have attached an example showing my data and to the right of it the chart. Currently the chart is set up with the data range specified as C2:O21. I want my chart to dynamically update when new rows of information are added.

I have searched and found lots of examples using the OFFSET function and I can create named ranges using this function (you will see some in the Name Manager). However I am having trouble applying these named ranges to my chart. The horizontal axis must be the column headings (year/period) and these never change, however when it comes to plotting the vertical axis I'm having trouble working out how to specify the category shown in column C and the values for each year/period.

A lot of the examples I have viewed have the data set up in a different way to mine and I can't work out how (if it's possible) to do what I need.

Any help much appreciated and I hope I've posted enough information.

Thanks,
Alex