That backing plate only needs to stay in place until the sprocket assembly is mounted to the camshaft. Otherwise, if it, the valve plunger and spring are set aside, they can all go back together just fine.
It is NOT the port for the center lock. You have to go way deeper to get to that. It is a related mode switching valve.
This has been covered in the past but all I've seen is misinformation. Look for item 13 on the functional diagram.
https://demos.starbase7.net/t3Portal...0558A001X.html