I am almost 100% sure that the CAT you are talking about is GMATprep2. If that's the case we are experiencing similar trouble. I have taken GMATprep many times and I found that GMATprep2 contains some really tedious SC's making its verbal part significantly harder than that of GMATprep1. I dont now neither why that is happening nor the correlation among GMATprep1, GMATprep2 and actual test, this is rather my observation as an experienced GMATprep user.
Also, I found that GMATprep2 has math section that is slightly (but very, very slightly) easier than that of GMATprep1. Maybe it is not easier at all but contains some questions that I'm comfortable with. Again, without any deep analysis of the cause, I observed that it is slightly easier for me to obtain Q51 on GMATprep2 than Q50 on GMATprep1. Of course, this difference is not so obvious and so severe as for verbal parts of 1 and 2. Verbal is, IMO, much harder on GP2.
Should this worry us? I don't know. I have no clue what is more representative of the real deal. Has anyone experienced something similar?
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