Excel 2010 Dynamic Chart with named Ranges

Hi,

I have a range of data that will change size over time for a weekly report.

Column A contains date range, unknown number of rows
01/04/13
08/04/13
15/04/13
etc...

Column B through unknown contains data (Headers in row 1 and data in row 2 onwards)
Sales Forecast, Cost, etc...

again unknown number of rows (some of which may have empty cells).

I've tried looking at named ranges and created:

Date =OFFSET(Sheet1!$A$2,0,0,MATCH("*",Sheet1!$A:$A,-1)-1,1)

Values =OFFSET(Sheet1!$A$1,0,0,MATCH("*",Sheet1!$A:$A,-1),MATCH("*",Sheet1!$1:$1,-1))

When I create a chart and enter
Horizontal Axis: =Sheet1!Date
Chart date range: =Sheet1!Values

The chart is populated with the correct data, but when new weeks or values (columns or rows) are added to the data the chart range doesn't expand to take these into account, the ranges are static?

Any help greatly appreciated.

Thanks

Paul

Have created an example file, attached. I can get the chart to dynamically change when use just 2 columns (A and B), but how to get it to include C & D and make them dynamic also?