I think I can help you - over the past two years I've been working on and have recently just published some new CEN review material as well as a CEN review course that we do on-site. Part of all the background research on all that included looking at the major/leading texts and resources that are on the market.
While there are many books out there (mine included) which have "CEN-like" exams in them, the only one that has "official" CEN questions in it is the ENA's CEN Review Manual circa 2004. The material in this book is
questions from previous CEN exams.
When the BCEN "updated" their exam in 2007, the old question bank was culled down and new questions put in. Now these "old" exam questions can be found in their review manual as well as the ENA online practice exams.
So in answer to your question it's "yes" and "no".
As one who has researched the main materials, the core curriculum and the CEN exam process, I firmly believe that the ENA CEN Review Manual most closely
replicates the actual CEN exam; both in scope of knowledge and in question type.
Now, you mentioned that you only got 73% - I'm assuming that was your overall score right? However, break it down into "systems" (OB/GYN/GU, Professional issues, patient management, Trauma etc) and look at the areas you did well in and not-so-well in. The main utility of taking sample "exams" is to find your strengths and weaknesses of certain sections, not really your overall score. So find out that information and use it to help you further refine/prepare for the exam.
Hope this helps.
Email me anytime if you need anything!