@svv1182 Since according to the Sibast family Grete Jalk indeed did design for Sibast and since a seller on the internet was kind enough to uplode a catalog page with a very similar chair and Jalk reference, I would assume it's safe to say: Jalk for Sibast. Although I have to admit that my first guess was Vodder.
And here you have a match.
"People buy a chair, and they don't really care who designed it." (Arne Jacobsen)
If you need any help, please contact us at – info@designaddict.com