Hi Cristina,
Thanks for the question. At this point, if you are taking the October LSAT, I recommend that you begin taking the LSATs that were given in the most recent years. The theory behind that advice is that the most recent tests are likely to be the most similar to the October 2013 LSAT. As far as differences between LSATs, let's discuss that in more detail.
The LSAT goes through broad but slow changes over the years. For example, recent exams have featured Logic Games sections that are--in general--easier than the ones seen on many of the tests in the 1990s. At the same time, Reading Comprehension on recent tests has been more challenging--again, this is a generalization--than on many of those same tests in the 90s. Eventually, we'll see those patterns shift again because this is how test makers keep test takers slightly off-balance.
That last comment is one worth expanding on. There is a constant arms race of sorts between test preparers (such as PowerScore) and the test makers (yeah, I mean you, LSAC). The LSAT slowly evolves for several reasons--including that once methods are widely known and effective for mastering certain concepts, the "yield" of those questions drops, and the test makers move on to different concepts to emphasize. For example, it used to be that you would see Logic Games sections with a fairly significant number of questions phrased in terms of falsity (Example: "Which one of the following Cannot Be False?"). However, in the Logic Games Bible and our courses we discussed how to easily handle that type of phrasing. The LGB alone is read by thousands and thousands of students every year, and so over time the test makers began to notice that the "False" questions weren't as effective as they previously had been. What did they do then? They slowly diminished their use, and these days you see "false" questions, but not that often. As students study recent LSATs (which are the only ones the average student typically looks at), they don't see many questions posed in terms of false, so it's not something they tend to worry about or really learn how to quickly handle. That will probably last a while, and then one day an LSAT will pop up with like 5 questions posed in terms of false, and a lot of students will not be ready because the false-to-true conversion is one they won't have spent much time studying for. This is why you have to prepare for everything--because you never know exactly what they will choose to emphasize on the LSAT you take.
Another example of how concepts come and go would be with Circular games (the ones where people sit at a round table). In the 1980s, Circular games popped up with some frequency, and handling those games was something most students were prepared for. When the new LSAT format (at the time) debuted in
June 1991 (see PrepTest 1, the last one on the page), the very first game was a Circular game, and most students handled it easily. And maybe they handled it too easily, because that was it for Circular games for a long, long time. The next one didn't appear until
October 2003 (see PrepTest 41), and after a decade-long absence, most students really weren't ready to effortlessly apply some of the special approaches you need to use in Circular games. Thus, the game caused a lot of trouble (and it wasn't a particularly easy game, anyway). After that exam, I remember a lot of students asking about Circular games, and making sure they knew exactly what to do in case one came up on one of the next LSATs. And what did LSAC do? You guessed it, a Circular game hasn't appeared since that test. At this point, they aren't on anybody's radar, meaning that one will probably appear again within the next few years.
So, the point is that the types of questions emphasized from LSAT to LSAT do change over time, and this one of the reasons we strongly advocate looking at as many LSATs as you can--it helps you prepare for anything you might see on test day. The fact that you've been doing tests from the late 90s will help you in general, but given the short amount of time remaining until the next LSAT, I'd say move to the 2011, 2012, and 2013 tests and knock those out since they should be closest to what you see in a few weeks.
Please let me know if that helps. Thanks!
