There are no overlaps with the OG books (though some overlap with some of the software/banks available for sale that I have seen, specifically old PowerPrep and Paper Tests).
The answer is that unless you need more official questions, you don't need them.
guide is not really enough by itself. If you mean "guides" do you mean verbal/quant workbooks too?
Thank you for your prompt reply bb. I have the 'Kaplan
New GMAT Premier 2013 with 5 Online Practice Tests' and 'The Official Guide for GMAT Review, 13th Edition'. Plus, I have the PowerScore CR
Bible and the Manhattan SC book. Do you think these books are enough to get a good score ? I am worried more about the Verbal section than Quant.
Any thoughts about 'GMATPrep® Question Pack 1' and 'GMATPrep® Exam Pack 1' ? Should I purchase these ?