I'm in need of the advice of those who own the Histories of Middle Earth books/collection. I have been purchasing the Histories books piecemeal when I come across a great price. So far I've been able to purchase Vols. I-VIII and X (which I haven't yet received). None of the books match in edition, date, etc. My question is, should I purchase Vol XIII, The History of Middle Earth Index or would it be a waste of money? I ask bc I don't know if a given Index aligns itself with its particular set or edition. Would the Index match-up with varied editions (e.g. page numbers, chapters)? Or does each edition have its own Index that cannot be disunited from the whole? Thanks for any advice given.