50-70s Vintage Floor Length Purple Dress

I bought this from someone who buys and sells vintage clothing and she placed it at the 70s, I am not sure how accurate that is. It's definitely old just by looking at the tags. It was kept in quite good condition since it has to be at least 50 years old if not older. The materials used are top notch. The only thing that sticks out is that there is some discoloration at the pits however when you are wearing it barely is noticeable. It is a deep purple and floor length (if you're 5'4" haha). It hits me right at my ankles which is nice, don't have to worry about tripping over it. I love the dress but I just don't have any opportunities to wear it. Also it has quite a bit of stretch. For context I bought this when I was a size 1 or 2 and now I am more of a size 2 - 4 and it still fits because the material stretches and it surprised me that it didn't feel super tight. I am selling other dresses because they do feel too tight for me now. It's about 54 inches long and has an 11 inch waist. Let me know if you have any questions. For more info on who made it: https://en.wikipedia.org/wiki/International_Ladies_Garment_Workers_Union