Jim,
There are normally two applications requiring a crush plate (may also be called a "face plate"). Our plane has a Warp Tapered tip with HPL hub on the front of a 912ULS.
1) In the case of a wood prop - to disperse the torque of the bolts evenly over the prop head.
2) With a spinner bulkhead (and that depends on the specific spinner). For instance, we installed a UHS spinner with a fiberglass bulkhead which is designed to have a crush plate on top of the bulkhead to lend it stability and to disperse the torque over the bulkhead rather than concentrating the pressure right under the bolt heads. Attached photos of the UHS spinner/bulkhead which required a single crush plate on top of the bulkhead.
I can't imagine any situation where two crush plates would ever be needed. You may have a case where the prop supplier provided one and the spinner people provided one, each as an accessory to their product - possible duplication which beats not getting any from either!
The final authority would be prop and the spinner supplier - any doubts might be a good idea to call up both of them.