With a threaded headset, between the cone and locknut, a single washer with the antirotation tooth is ideal.
However, if there is no room, you may use a pair of cone wrenches, and torque the cone and locknut against each other to prevent loosening. -same as method in most hubs


additional important note
you wanted 9?mm?(did you mean cm?) of spacer between the cone and locknut?
WHY?
Were you attempting to use a longer than normal steerer on this frame; perhaps as a means of setting the stem higher?
You do realize, that this is not a safe thing to do on a threaded headset, right?
The minimum insertion mark on a quill stem, is in reference to the effective top of the headset; ie, the cone. Adding a stack of spacers above the cone, does not mean you get more height. Any threaded section of steerer above the cone does not support load safely; the threads act as stress risers and can fracture.
1 antirotation washer; that's it, no spacers or other wierdness should be in there.