If you see the study material or the suggested answers for IPCC and final exams the institute has put a disclaimer that due care has been taken in preparing the material but the institute is not responsible for the corectness of the answers. For the suggested answers it clearlys states that the papers are not corrected on the basis of the answers given in the suggested.
Having said that I would suggest that if you get a different answer do not automatically assume that the answer in the study material is wrong. Only a few answers may be wrong. First you should be sure that you have the right answer before you draw such conclusion.