Hi Aussiebear. This link has the manual way to show hidden cells and some interesting VBA that you might want to trial....
How to show hidden data in Excel chart - Excel Off The Grid
Sub ToggleChartDisplayHiddenRows()


'Declare and assign variable
Dim cht As Chart
Set cht = ActiveChart


'Ignore errors if no chart active
On Error Resume Next


'Toggle hidden data visibility
cht.PlotVisibleOnly = Not cht.PlotVisibleOnly


On Error GoTo 0


End Sub
HTH. Dave