It is true, because if an oil passes the 0w cold cranking tests, then it obviously has numbers good enough to pass the 5w and 10w cold cranking tests too. So legally a company could have a 0w40 oil on their hands and repackage it as both a 5w40 and a 10w40 and a 15w40 if they wish.
It's been pointed out on here before that Schaeffer's 15w40 could actually be labelled a 10w40 if they wish, since it's cold cranking numbers are good enough. But 15w40 is a more popular viscosity to the types of clients they typically deal with.