Summer Maxi Dress Deep Aqua TieDye 100% cotton Flowy Pullover Sizes S and M

Summer Maxi Dress Deep Aqua Sea Design, 100% cotton Flowy Pullover Sizes S and M P to P is 19” for both and the length seems the same. These are local finds, I have two of these. One is marked Small and the other is marked Medium and I can’t measure any difference. Perhaps there’s more room in the bust in a medium? They should fit comfortably as they would be a great summer casual dress or something to pack and wear after a day at the beach.