NWOT Jill Jill Stuart Navy dress 12 but fits like an 8-10

Bought and never worn so it’s time. Beautiful navy dress with a heavy crepe like fabric. Pleats begin as darts in the bust and turn into pleats in the skirt. This is a size 12, but it really fits like and 8-10. It was big on my mannequin which is a size 6. Absolutely no flaws. See pics for measurements. Smoke free home