Scrump: the reason you shouldn't call your song written today traditional is simple. It may be written in a traditional style, but it hasn't become traditional yet. Same reason you'd be tempting fate in looking at a baby and calling it a man or a woman. That takes time, and there's many a slip twixt cup and lip. The new song you refer to may be brilliant, but that doesn't make it traditional. Time alone can do that, and many people.