Vintage 60-70s Union Made Womens Plaid Sleeveless Modest Back Zipper Dress S/M?

Vintage 60-70s Union Made Womens Plaid Sleeveless Modest Back Zipper Dress Nice vintage condition, has a few small faint spots/marks, no rips, holes or tears, dress has no brand/material/size tag, does have a union label, some smocking and stitching along front chest, back zipper, sleeveless, estimating size S/M, but please see photos and measurements below Dress form in photos is a medium form with a bust of 34.5" Approximate measurements while laying flat Armpit to armpit - 18" Length - 37.5"