Sharp There is talk at GMAC about introducing a detailed post exam report(link at the bottom). They are still working on the details, however the exam report would be the same as the information that was recently added to the GMATPrep Free Practice tests. Perhaps this would be one way to answer these discrepancies. In general, I recommend taking the official GMATPrep tests under conditions as close to the real exam possible(for example a quiet place in a library, and taking the entire test in one sitting). I have never seen much of departure from GMATPrep tests and official tests when a student has implemented this approach.
Here is the excerpt from mba.com:
Enhanced score reporting for all completed exams in GMATPrep Exam Pack 1.
The Quant and Verbal score report provides results by question type including, user score, mean score, and percentile ranking on each subsection.
The IR score report includes user score, percentile ranking and time management reporting.
Valuable time management reporting to gauge your pacing
Enhanced score reporting will also be available for free exams with the purchase the GMATPrep Exam Pack 1."
Link about the new GMAT reporting:
gmac-annual-summit-188582.html#p1442904Dabral