Same subject and authors but different books. Which one to buy?

There are quite a few changes in NANDA 2009-2011 vs 2012-2012 including diagnoses that have been added, changed, removed, reclassified. You don't want to use a nonexistent nursing diagnosis.

There's another thread asking whether there are "huge" changes in NANDA-I-- short answer, yes, there are changes, yes you should always have the current edition, and yes, buy the NANDA-I 20112-2014 itself and whichever other you like better.

There's another thread asking whether there are "huge" changes in NANDA-I-- short answer, yes, there are changes, yes you should always have the current edition, and yes, buy the NANDA-I 20112-2014 itself and whichever other you like better.

Wouldn't all of the NANDA information already be in those diagnosis books though?

I still don't get why the same authors wrote books on basically the same material. I must be missing something.

The NANDA-I is copyright and while they do grant permission to quote and use some of their material in texts and periodicals, they charge for the privilege and never grant rights to completely reproduce their entire work. In addition, they do make changes in the content from time to time, as noted previously. Therefore, no, no textbook will include all the current material in NANDA-I, and your best bet, by far, is to get the book in its most current edition. It's not that expensive, really.