I was asked for pics of the sides and back of the Oseberg chair.  Here they are.  The back is one piece, so it comes off in a unit.

As for why there are no holes in the back for the seat weaving.

This particular one won't have a fully woven seat.  The holes in the front and sides are to mimic the action of a woven seat.  The buyer didn't want to re-weave a seat every time she broke the chair down.  There's a plywood seat that she is padding and covering.