Your chairs look like it could be related to the "Morten" model designed by John Mortensen in 1983.
Koefoed seems to be still around. Maybe you could ask them directly? (If you do so, please don't forget to share the answer with us!)
Lauritz also had a pair of them but yes, they are indeed pretty unusual.
http://www.lauritz.com/sv/auktion/niels-koefoed-moebelfabrik-spisestole-...
I hasten to add to this conversation that rare=/=valuable. The later Koefoeds designs really aren't that desirable because they aren't as dainty or lightweight. Lacks much of what defines the popular idea of Danish modern.
I do remember reading similar heavier designs by Koefoeds attributed to John Mortensen and it was late 70s at the earliest to fall in line with Dr Poulet's information. I don't think it's a far reach.
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