I have not yet written any part of SCEA, based on what I have been reading in this forum, your answers to questions in part-III are based on your part-II design.
Since Sun prometric exam confidentiality agreement prohibits candidates who have completed part-III from disclosing the actual questions, we will never find out if the questions are same or different in part-III, but I think the questions in part-III is not same for everyone and depends on your part-II design.
The questions in part III are quite generic. You have to refer to your part II solution and explain/justify some of your design decisions. If you know your part II solution and have done reasonably, part III is a no-brainer.
Only purpose of part III is to make sure, that it was in fact YOU who did your part II solution