ASOS Deep V-Neck Black Midi Dress Elastic Waist Short Dolman Sleeves Versatile L

Dress from ASOS. Size is marked US 4, but I wear a 12 (I am 5'7") and this fits me perfectly. I am wondering if it was missized. Thick, quality fabric. Has elastic at the waist and a hook and eye clasp on the v-neckline. Worn once to a rehearsal dinner. No flaws. Measurements (taken when laid flat): Armpit-Armpit: 16" Waist (not stretched): 12" Length: 44"