I can't speak for the students, but I was an incorrect solver too (2 errors), because of a lack of tidy record keeping and double checking...
I have reviewed enough exams and "clever" exams to know that neatness isn't the deciding factor in the results. This particular problem has a myriad of redundancies built into it, and an answer checker to boot. Can you show us your work Richard and how two errors made it to the end?