NWT shift dress black sequin, marked L but fits like S

Sleeveless, high neck, black sequined dress with keyhole back. The edges are all bound with soft fabric to prevent the sequins from poking you. Fastens at the back neck with two buttons. The synthetic knit fabrics of the outer dress and the lining fabric have stretch, but this dress isn’t large, even though it’s marked L. Mannequin’s measurements are 34/26/36, with a B cup. The dress fits her. Never worn. Has tag and spare button. Pit to pit 17”. Back length 34.5”. From a smoke free and pet free home.