The shoulder boards are sewn into the seam from inside of tunic(under the liner). I think that the sutures were placed through the braids, instead of inbetween. This would prevent the boards from coming out/fraying. Basically, the inner liner would be opened from around the top of the sleeve. The top of the garment sleeve seam would be opened as well. The board would be inserted and the tunic cloth would be folded around the board and sewn to the board, from inside the tunic. Once this is done, the inner liner would be closed.