I was only looking at the graphs for all ages. EDIT: Ah OK, I see what you're saying. Yes, my statement that the cumulative graph is defined to be monotonical

I was only looking at the graphs for all ages. EDIT: Ah OK, I see what you're saying. Yes, my statement that the cumulative graph is defined to be monotonically non-decreasing was indeed incorrect because it assumes that excess mortality itself is non-negative, which is not the case (total mortality would be non-negative though). Still for the cumulative graph to decrease the weekly excess mortality would have to go into negative territory, which is far from the case for the "all ages" group.