It is not the neck which is applied to the decanter, but a bottle in half post technique. Because the body of a bottle requires a lot more glass than the neck, the paraison is covered in a second layer of glass before being blown out.
The cork stopper with the pierced coin is a typical Scandinavian way of closing decanters. Such items have been made by nearly all Swedish (Danish, Norwegian) glass makers - Skruf jumps to mind for this one. Often coins were used which allow dating - but sometimes just plain rondelles.