Than is true. All version of QR are same. All version of OC is totally different. All version of GC and BIO have big difference. (NOTE: I checked all versions from 2010 to 2013. I did not check the version before these).
Although they have big difference, the knowledge that the questions covered are almost same. They just put the knowledge with new question.
So, read old versions are not that bad. Of course, if you read all version, that will be much better I am not kidding, I read three versions 2010, 2011, and 2013.
If you have time and money, read 2012 and 2013/2014 will give you more practices on the same knowledge.
This sounds great. However, the new problems keep coming up on the DAT with new topics. I think, if you have almost a year before take the test, many new questions will come up on the new topics. So, an updated version of the book may be a good idea.