Knoll and Shepherd Ball Casters  

Hi Design addict,
Does anyone out there know when Knoll used ball casters from Shepherd on their chairs? I recently picked up a Pollock office chair with these casters, and I previously had some saarinen armchairs with these casters. I'm just trying to date the pollock chair. Seems like Knoll used these in the 1960s.
The Pollock chair also has an older Knoll label on the bottom, the rectangular label with the text running horizontally that says "Knoll international." I'm attaching photos of the chair, label, and casters here.
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