Butt plates only came from Ordnance as a complete assembly like Bren change levers. Maybe they've just had a load of parts or stripped a load of complete assemblies down to the individual components.

Reminds me of when I saw a zillion used Mk2 Bren backsights. Yep...... each one stripped down to its component parts! For what? The only thing that ever wore out so far as I remember was the detent clicker spring.