Vintage deadstock brown white floral dress

Vintage no flaws found still has its original NWT brown and white 100% polyester dress. It says it’s a size 18 1/2 but you know vintage sizing and how crazy it is. My best educated guess would be closer to about a size 10. Please go by measurements to be certain of fit however. Does come with a belt and buttons up 1/2 way. It has a sweet little tie around neck area. Under arms across chest 21 1/2”, across back shoulders 16”, overall length is 39” waist about 21” across.