Nokoreach is the national anthem of cambodia

The cambodian national anthem was written by Chuon Nath (off wikipedia.com) and I have not yet discovered in what year but I think it was around the 1940's if anyone can answer my question it would be deeply appreciated. Question: When was the Cambodian National Anthem: Nokoreach written.

I am pretty sure it was written around the 1940's but then it was changed but then it came back at around the year 1950's. I have no idea other wise as it says on all the websites I've visited, (one was even Wikipedia) it said nobody actually knows when the 'Nokoreach' was written unlike some other national anthems!