this is how merged reports used to function, now it opens in new tab and will remove any pending changes if you complete the edit on the merged tab window. So it find it best to always save the dashboard before editing a merged report. very clunky.

glad this worked for you, it would not for me bc i cannot edit the LOOKML. I was hoping to do it with just table calculations alone.

Unfortunately, I have not found a solution to this. I needed this as well. This would work if we could set a parameter of a match type that output the last occurrence (like excel).