Technical Rear Hub Lock Nuts

[criceo]

I'm striping my car's suspension, and I'm confused about the castled nut on the rear of the hub. The manual says it's a 17mm nut, and FDRicambi sells an 18mm nut. However, the nut on the passenger rear of my car is much larger, around 23mm. The Haynes manual shows a folding plate that goes around this nut, but I don't see it on mine. Am I not understanding something here?

Also, the Haynes manual says that the coupling boot that slides over the splined end of the axle and that bolts into the hub coupling sleeve should only have three bolts, but mine has four.