Taz, you have to work with people who don't know that they're the same thing! How unfortunate for you. Though I do remember that on my first reading of LOTR I thought initially that they were only Nazgul once they were airborne, as that's when the word becomes more common in the text. Mind you, that's also the point where Tolkien abandons any pretence of using easy language and gets all grandiose and biblical about it.
http://www.plasticsquirrel.co.uk for all your bizarre music and musings needs