Formulas not updating
 

I have several cells in ColA that use the following to get a total from
ColAB:
=SUM(INDIRECT("AB4:AB"&ROW()-1))
AB4 in the formula is different for other cells in the column to total
seperate blocks of data. Blocks of data contain same number of rows, so
this works fine.
Problem is when I run a routine to insert another block of data and then
sort the sheet, the INDIRECT range doesn't update and some of my totals are
then incorrect.

How to fix?

--
David