We don't have a separate, second question database, so if you want to use our tests, you will need to keep using the same product / database.
If you haven't looked at these questions in >6 months, though, then chances are good that you will have forgotten most of them. (You also won't have seen all of the questions - so you will see some new ones. We've also added at least 150 new questions in the past year.)
What I'd recommend doing is going ahead and taking one test. If you see more than 3 questions per section that you remember (not just a vague sense of familiarity - that's okay), then you should use a different set of tests.
You can still take both GMATPrep and MGMAT CATs with a few repeats as long as you follow some guidelines to minimize the chance of artificially inflating your score via question repeats. First, anytime you see a problem that you remember (and this means: I know the answer or I'm pretty sure I remember the answer, not just "hmm, this looks vaguely familiar..."), immediately look at the timer and make yourself sit there for the full length of time for that question type. This way, you don't artificially give yourself more time than you should have. Second, think about whether you got this problem right the last time. If you did, get it right again this time. If you didn't, get it wrong again. If you *completely honestly* think that you would get it right this time around if it were a new question (even though you got it wrong last time) because you've studied that area and improved, then get it right this time.
Finally, I think this would be a good resource for you:
http://www.manhattangmat.com/blog/index ... -the-gmat/As well as this new article:
https://www.manhattangmat.com/blog/inde ... lly-tests/