Is my grandmothers eveninggown from the 40'ts?

I call this the Morticia Adams, problem is that their no label, no markings of any kind. I think it was fitted for her, since I have another one, same model, no markings. The fabric feels a little bit like crepe, like it should be "strechy" but it isn't. There's a cleverly hidden zipper at right side of the waisteline
Please help.

 

Hi Maggie and thanks for your answer.
Oh dear.
I thought I did?!
Ok, I'll try again, please let me know if it doesn't work out this time either!

 

Thank you.
Apparently I can't upload them from my cell.
Darn it!
I'm so sorry!
I'll find a way to transer tgem to my laptop and go from there.
Thank you so so much for letting me know!
Nina.

 

Ok, here we go again. Sorry for all the fuzz.

 

Nina, what does the zipper look like? Do you have any photos of the seams and/or hem on the inside?

 

Yes, I will upload additional photos in a minute.

 

So sorry for the late reply. I sawit in the wee hours (time difference and I´m a nightowl) and there wasn´t light enough for my very poor ability to take pictures.
Will upload new ones of the zipper in a minute.

 

Thank you.

 

Will add photos now.

 

Here, some new pics of the zipper and the shoulder pads.
I alsofound this odd blye stitches, but I have no idea what they mean?

 

Are the zipper teeth metal or plastic? It could also be a replacement zipper.

 

It's metal. I also saw, for the first time, that it's way too long, so maybe a replacement or as a previouds thought, added after the dress was made.

 

I don´t know what happened and I´m not very good at this, for some reason alerts and notifications didn´t show up for 48 hours and I´m so very sorry and apologuise to all you kind people who answered me.
So let me try this once more.
The zipper is far longer than "needed", the shoulderpads are made of a material I´ve never before seen.
Neither the hem nor the seams are sergered.
The blue stitches I found while turning it inside out, still puzzles me.
The material is still an enigma, I feels a bit like crépe, like it should be a little "stretchy", but it isn´t.
I still think it was fitted for her, since I have another (heavy silk) one of almost identical cut.
I really would like to know how old it is, if it´s from the 40´ties or perhaps the 30´ties?
Oh, it could have been made here in Sweden, or in Britain where she spent a lot of time.
France and Usa are also a possibility but less likely since she wasn´t as much there.
Please help.