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http://www.youtube.com/jhempel24 said: Star Wars did it perfectly with the whole Quick Glance Icon thing. You aren't going to have a perfect timeline in order to squeeze things in between other books in the future and keep the same numbering system, it would just be too complicated and turn people off. Lets face it, for most people, numbers are scary.
Your best bet is to keep a timeline in the book, and as new-er books come out, just update the timeline but always..ALWAYS point people to the website for the most up-to-date timeline.
As for eBooks being updated, I doubt that everytime a new book comes out each vendor is going to want to deal with uplaoding a new book to their system and then having the customer download it. Especially, for people like me, who will download it, and strip the DRM and organize in Calibre for reading on any system I choose and not be locked down.