A single, multiple or all columns at once, note and/or effect columns can be changed within one single operation and thus will result into one notifier call too. That’s why the notifier can’t provide that info.
I see where this suggestion comes from though. You need this for this tool here, don’t you? New Tool (3.1): FormulaOne
Then you’d actually need a different kind of notifier: One that only fires, when the user directly enters or records a new note or effect column value. Right now the notifier will also be called when cut/copy pasting, doing something in the advanced edit, on undo and redo and when other tools write into the pattern. Those are all scenarios where you don’t want to apply your formulas. If you do, you’ll actually will start breaking those other changes.