Update unknown number of grid records

I have multiple orchestrations where I need to update an unknown number of grid records as processed.  I actually need to update all rows...but one.  The Select All Rows option would normally work perfectly but this grid always includes one blank row at the bottom for adding new data.  For example, if there are two detail lines for this document, the grid will have 3 rows in it.  The first two for the existing data and a third for the potential to add a new line.  Using Select All Rows updates the two existing and also populates the third row