The trials should be load in the order they were run, this is the TRIAL:TRIAL_NUM parameter. You could sort by just the TP and there are a number of ways to do this. The quick and dirty way I just found is a script like:
exam_data = zip_load;
for idx=1:size(exam_data.c3d, 2)
exam_data.c3d(1, idx).TP = exam_data.c3d(1,idx).TRAIL.TP;
The nestedSortStruct came from this MATLAB article:
Please let me know if that helps.