I have 20+ bookcases full of books -- some of which are referred to in the TOG Y2 Classic and Redesign, but most which are not. Just how hard is it to use a lot of books on the same topic but that are not specifically mentioned? For example: I have no less than 10 biographies on Columbus at various levels - only the lower grammar level one is one recommended in TOG. How much am I going to mess up my 4 kids if I assign them different versions of Columbus' bio? Same goes for other biographies and general info books... Can I just hope that they'll get what they need and ask my dialectic age daughter to do extra study to answer questions she may not have found the answer to in her readings?