I'm trying to put an approval history table on a form that tracks date, user, decision, and comments. The decision itself is made via dropdown list, so I'm trying to use a field calculation to populate that column. However, changes made on later forms change not just the current line of the table, but all previous decision values. This is with the option to make previous data read-only. In the screenshot below, the first row's Decision should say "I Approve".

Is there a way to use a field calculation to populate just the current, editable row and not previous read-only rows? I'd prefer to use calculations rather than JavaScript if possible.