I have a 1931 coupe. The drivers side door handle
The mounting plate that is screwed to the door was held in place with a cup and spring. The cup shaped washer was held in place by swedging or pinching the corners of the square handle shank. This kept the handle from slipping out of the mounting plate. Some repo handles had the square shank cross drilled and a pin inserted to hold the cup and spring in place. See the attached photo.