centerlock to 6 bolt adapters--missing part?

I bought some NOS American Classic centerlock-to-6-bolt adapters off fleabay. What came was this:

 
I have another set of them in use on another wheelset. What that set has that this lacks is a metal washer/shim with six holes in it that goes in between the rotor and the piece that you screw on. As pictured here: American Classic CenterLock to 6-Bolt Adapter | eBay. I tried to install a rotor without that piece, and it really seems sketchy to me. Am I correct to think that that's a necessary part? Or should I not worry about it?

if the rotor is tight, you don’t need the shim. IIRC the very similar DT version does not have a shim

OK, good to know. I'll try to crank them down to 40nm and see (tentatively) whether they'll kill me.

Yeah, I asked the same question over on mtbr. Some people said not to use it, but others said this is just a different design and if I torque it to 40Nm it should be fine. Also that it would be pretty obvious if it didn't work.