Using the following to define the dynamic named range

=OFFSET(IAMT!$G$8,0,0,1,COUNTA(IAMT!$8:$8))

Not sure how to check the returned value

The SUBTOTAL function I am using seems to be returning the correct total value (i.e. if I add additional values then the subtotal is updated correctly its just the correction for hidden columns that doesn't appear to be working