not all of the classes as shown in the handbook are present 
Happens a fair bit from my experience, especially tutes, but sometimes pracs/workshops. I have a subject where the handbook says there was a workshop Monday-Friday, but the timetables only have Wednesday-Friday available.
The handbook lists most potential classes, but since the handbook timetable is made in October last year (from memory), staffing issues and numbers limit how many classes they end up offering. Keep an eye out though, some classes tend to pop up if the existing classes fill up, and there's not enough existing slots.
My timetable was done by 10.10am while on the exercise bike at the gym, multitasking ftw!