When is a book alive, and what if you have the dead version?

My head’s spinning a little right now.  Just had a visit from someone in our DocDel dept. who was trying to track down a chapter from the 2nd revised edition of Encyclopedia of Biopharmaceutical Statistics, which our catalogue says we have through Ebrary.  Except that the cited chapter had a publication date of 2006, while the 2nd revised edition Ebrary has is 2003, the original publication date.  Odd.

A Google search on the chapter title leads to a page on Informaworld, but has a publication date of 15 August, 2006.  backtracking to the main page for the publication shows an Original Publication Date of 23 April, 2003, but a Last Updated date of 23 April 2007.  And there’s a tab at the top leading to Recent Updates, which means this book is not a static title, but a dynamically-updated one. 

On the one hand I love this idea, this is how to keep things up to date.  On the other hand, we purchased this title from Ebrary, not Informaworld, and as a result we have the dead version of the book, and thus no way to access the chapter requested by our patron!

This is the first time I’ve run across this – is it more common than I realize?  I wonder if the Informaworld version was more expensive than the Ebrary version we bought?