Thank you for your replies.
I found this topic Some pics of my mint M1 Schlueter shell
and I think my M1 is really similar to those helmets.
You can see a dimple in the inside edge, maybe used for positioning the chinstrap bales. I think that's what rudder means?
The helmet in that topic is mine, it's an untouched, mint original Schleuter and an excellent guide for the correct colour and texture. I think your helmets are fine and possibly re-issued for Korea and/or Vietnam, although they seem to have their original WW2 paint.