H&M black sundress size 42 fits like American small/medium

I have another print of this dress in my closet and you can see the details better on that one bc it’s not black, it’s floral. This dress has a ruffle around the top hem, a tie string high waist detail, tags are cut out. I personally bought this in Europe many years ago, that is why the size is 42 but it fits like a small/medium in American sizes. The sizes have become more generous over the years. It does not fit like a current 42.