After I damaged the threads on my 1986 Peugeot threaded steel fork a few years ago ("operator error"), I had a frame builder repair the damage by cutting off the old steerer tube and welding a new one back on. At the time he asked me if I wanted a groove put back in the new threads as per original. That's the groove that runs longitudinally down the fork steerer tube threads to locate the tang of a lock washer between the top race and the top nut, as I believe per standard French fork practice (?). For whatever reason I can't remember, I said "no".

So I can't now use a tanged lock washer.

Will simply tightening the top nut down onto the top race be enough to stop the headset loosening?

Or do I need to be considering additional ways of stopping the top nut backing off when the bike is ridden.