Jens Risom for Knoll??  

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Hi, here are some pics.  

Pics

Pics

You're right to be suspicious. Some details, such as curved front edges of seats and tops of seat backs, position of leg/seat frame joints, and general proportions seem off.

The original design is Jens Risom, from the 650 line he did for Knoll in 1943.  It was later produced in Germany as well by Walter Knoll as the "Vostra" chair.  I agree that these look different than the genuine ones I looked at online (see photo from Walter Knoll).  The ones in your picture are more upright, more of a dining chair.  

Risom's 650 series were designed only as lounge chairs not dining chairs.