Help identifying 1960s(?) criss-cross-patterned dress

[196t's]

Good morning/afternoon/night,

I'm looking forward to starting my own online business. I am based in Brazil, so I planned on buying vintage clothes here and selling them worldwide through eBay. I've found other dresses that I'll be posting here soon, but let's start with this one, shall we? The seller says it's vintage. It has this criss-cross, dark blue and red with white squares pattern, with a back middle zipper (common in 1950s and 1960s dresses) and it's sleeveless, even though not a scooter (pff, obviously). So, these are the flags that indicate it's from the 60s, based on my experience (pattern, back middle zipper, sleeveless). I don't have any pictures from the tag, and even if I had, it probably wouldn't help much, since it's (likely to be) Brazilian-made.

Any help is appreciated. I only need confirmation if it's really from the 1950s, '60s or '70s or if it's fake vintage. Thank you for your time and willingness.

Update: Just asked the seller, they said the tag is from International Ladies Garment Workers Union.
Update 2: Added the tag's picture.

 

[Vinclothes]

What kind of fabric do you think is made of? That may help with dating.
Marian

 

[196t's]

What kind of fabric do you think is made of? That may help with dating.
Marian

I would guess it's polyester, but I might have some info that would be more helpful. I asked for a picture of the tag and according to what I've researched, it was probably made between 1964-1973. Just need some confirmation.

 

[Vinclothes]

I believe it is early 1970's. Dropped waists were popular in the late 1960's into the 70's.
Marian

 

[196t's]

I believe it is early 1970's. Dropped waists were popular in the late 1960's into the 70's.
Marian

Thank you! Much appreciated. I've also heard they were popular in the early '80s, but this isn't the case, anyway.

Thanks again!