PR prep books for SAT II Bio and Math

<p>Hi everyone. Is there any sense in buying 2008 edition PR prep books if I already have a 2002 edition book for math and a 2006 for bio?
Are there any changes in them except for the practice tests? Do the core concepts remain the same?
I'm asking that coz I'm not from the U.S., so the only way to get those books is to order them from amazon.com, and therefore pay for shipping of each book I want... =(
Thank you in advance</p>

<p>bumppp.....</p>