Without wanting to sound too dumb, how many variations of the A4 were there?
Mine is like the one in the pics, others I've seen have one thumb screw, others still with a much deeper butt hook ....
Aces, old school McMillan A4's has the angled hook in the butt portion. Newer A4's are all parallel to the forearm. Recently McMillan switched from the two screw cheek piece to a 1 screw design.