According to Ball, anything produced after 1915 should have grasping grooves. Does not give a specific date of the disassembly hole but those produced in 1918 are shown with it. They also were re-stamped/issued in 1920 which mine was not. How do they attach to the stock, I never did anything with them before.
Ball only devotes three pages to the KAR98a. Not much to go on.