What is the design secret of the pull ring of cans?

The general manufacturing process of pop-top cans is to punch the bottle body and the bottle cap separately, and the pull ring on the bottle cap is punched separately before the bottle cap is closed. The shape of the tear is also pre-cut and perforated. After filling the contents, align the bottle body and the bottle cap, and then combine them into one. In addition to the fitting structure between the bottle body and the bottle cap, there is also a concave "buffer zone?" It is used to control the manufacturing accuracy, so the tear shape of the pull ring can not be attached to the edge, can not be cut to the concave part, and can not be cut to the side, which will bring unnecessary technical difficulty and cost increase to the manufacturing.