Quite so; when I said "safe", I could equally have said "reliable". There can indeed often be other evidence to suggest an approximate age, but, as I said, in the absence of such evidence no reliable estimate can be made, so it is generally better simply to say so rather than confuse people by speculating. People so often assume traditional songs to be older than they really are, that a little push in the opposite direction may at times be a useful counter-balance.