The rear end might have a special thinner clutch disk there for needs the extra one.I have a old rear end I snaped a axle out of and have new gears and bearing kit to do the junk yard one I put in.I was thinking instead of replacing the disk if worn putting in a extra one.Maybe that was done.Police cars need traction to save on tires for quick take off(hot pursuit hah).The original might have been shot and instead of replacing all they did what I plan to do.