Just check the year. 2003 marked a major change for the MCAT. If your material is after the change, it should be somewhat consistent with the difficulty level of today's test. The passages will, however, be longer because in 2007, the test was changed from 8 hours to 5 hours. Ultimately, I would not recommend using anything before 2007 as your primary source for practice tests. There are so many good up to date materials out there that would be more appropriate at predicting your performance on the current MCAT. These old materials are not useless though as they could serve as good supplements.