It looks to me like the knob fits inside the center circle of the disc, just inside the perimeter ring that contains the mounting screw heads. I can barely see what appears to be one of the screw heads butted up against the outside perimeter of the knob greeblie on the lower right hand side of the knob.
Forgive the crudeness of this approximation to illustrate what I am describing as the approximate first diameter of the greeblie knob sitting inside the mounting screw ring on the disc (below):
View attachment 799124
I imagine with only glue holding the knob greeblie onto the disc, that the knob survived only a few pulls out of out of a holster before the glue (like the glue on the lightsaber t-track) failed and the greeblie knob flew off into the snow.
The original knob greeblie is probably still buried in the snow in Norway