Each one is a step forward.. Includes more and new "stuff" and information.... The older books are really essential works as they set the foundations... but if you use the Bowen book as example, ground breaking and fantastic as it was for its time... the Wernitz book leaves Bowen behind, a collectors item, but maybe no longer "needed" as far as EK research goes. That is absolutely not a negative reflection on Bowen... he was the Wright Brothers of his time... Wernitz may be the F-18 Fighter plane... without the Wright Brothers there would not have been a F-18...
Best
Chris