Hi junii,
The 'pool' of questions that comes with any individual practice CAT/mock generally stays the same, meaning that if you took all of those CATs before, then there is a reasonable chances that you would see some 'repeat' questions if you chose to take those CATs again. Unfortunately, seeing even a couple of repeats can 'throw off' the Scoring Algorithm and impact your pacing, energy levels, fatigue, etc. (meaning that they would likely all appear to be better than they actually are). Thankfully, the Official GMAC CATs - along with those CATs from Kaplan and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you correctly take the CAT in a realistic fashion that matches the parameters that you will face when you take the Official GMAT) - so you can use any NEW CATs from any of those sources next.
A CAT is really a 'measuring device' - when used correctly, it will give you a realistic score and help define your strengths and weaknesses, but it will NOT help you to fix any of those weaknesses. To raise your scores, you have to learn the necessary Tactics and put in the proper practice and repetitions. The CAT will show you whether your studies are helping you to improve or not. In addition, the process of taking (and reviewing) a CAT requires a significant amount of energy and effort - and takes time to 'recover' from. This is one of the reasons why you typically shouldn't take more than 1 CAT per week - and your last CAT should be taken about 1 week before Test Day. Going forward, you really shouldn't take more than 1 FULL CAT per week.
Before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) Have you taken the Official GMAT yet? If you have, then how did you score (including the Quant and Verbal Scaled Scores)?
2) When did you last study - and how long have you studied in total? Have you done any studying recently or are you planning to restart your studies?
3) What study materials have you used so far?
4) On what dates (or approximate dates) did you take EACH of your CATs/mocks and how did you score on EACH (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
5) What is your overall goal score?
6) When are you planning to apply to Business School and what Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich